Orthopedic implant having a crystalline calcium phosphate coating and methods for making the same

ABSTRACT

An orthopedic implant having a metal surface and a calcium phosphate layer disposed on at least part of the metal surface is described. The calcium phosphate layer has an average crystallite size of less than about 100 nm in at least one direction and dissolves for more than 2 hours in vitro. The calcium phosphate layer is substantially free of carbonate. The coating, which is formed on a sodium titanate surface, has increased shear strength and tensile strength. The coating is formed by a solution deposited hydroxyapatite process under inert conditions. The pH of the solution varies by less than 0.1 pH unit/hour during coating formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 15/472,189, filed Mar. 28, 2017, the entire disclosure of whichis hereby incorporated by reference.

Cross reference is made to copending U.S. patent application Ser. No.______, filed Dec. 23, 2019, which is a divisional application of U.S.patent application Ser. No. 15/472,186, filed Mar. 28, 2017, each ofwhich is entitled “ORTHOPEDIC IMPLANT HAVING A CRYSTALLINEGALLIUM-CONTAINING HYDROXYAPATITE COATING AND METHODS FOR MAKING THESAME,” and each of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to a calcium phosphate coating,and more particularly to an orthopedic implant having a solutiondeposited calcium phosphate coating and methods for making the same.

BACKGROUND OF THE INVENTION

Bone repair often involves the use of orthopedic implants to replacemissing bone or support bone during the healing process. It is typicallydesirable to coat such orthopedic implants with osteoconductivematerials to encourage bone growth or biological fixation.

Hydroxyapatite (HA) is a naturally occurring mineral found in bones andteeth. Studies have shown that HA is osteoconductive, and orthopedicimplants have been coated with HA for this reason. Octacalcium Phosphatehas also been reported to be osteoconductive. Various processes forcoating implants with CaP and HA are known. One process used for coatingimplants is plasma spray. In this process, HA powder is fed into a hightemperature torch with a carrier gas. The HA powder is partially meltedand then impacts the substrate at high velocity whereupon it is rapidlyquenched back to room temperature. This process produces a mixture ofHA, other calcium phosphate phases, and amorphous calcium phosphate.These phases have wide differences in solubility in vivo. As a result,plasma sprayed hydroxyapatite (PSHA) films do not uniformly dissolve ordegrade in vivo. This non-homogenous degradation can generateparticulates in the vicinity of the implant which can result in aninflammatory cascade leading to osteolysis. The particles may also findtheir way into joint articular surfaces, resulting in increased wear.Finally, the process is not well suited for coating porous structures ofcementless implants because it is a “line of sight” process. PSHAprocessing or post processing methods can be applied that result inhighly crystalline coatings with long resorption times in-vivo. Thisattribute gives rise to concerns over long term delamination of theserelatively thick stable coatings.

Other methods to produce HA coatings for biological fixation includephysical methods such as sputtering, evaporation, and chemical vapordeposition. These physical methods do not reproduce thenano-crystallinity and high surface area of biological apatites, and theresulting coatings may not uniformly dissolve and may releaseparticulates.

Solution (or suspension) methods for producing HA coatings have alsobeen attempted. For example, Zitelli, Joseph P. and Higham, Paul (2000),A Novel Method For Solution Deposition of Hydroxyapatite Onto ThreeDimensionally Porous Metallic Surfaces: Peri-Apatite HA describes aprocess that involves producing a slurry of finely divided HA particlesinto which implants are placed and coated by accretion of the slurryparticles. High surface area, microcrystalline coatings are produced,but their adhesion to the substrate is poor.

Electrochemically assisted solution deposition has also been developed.In this process, a voltage exceeding that necessary to hydrolyze wateris applied to an implant while the implant is suspended in an aqueoussolution. This process results in deposition of calcium phosphatematerial on the implant. Typically, the deposited film is a mixture ofcalcium phosphate (CaP) phases and requires post processing to convertthe films to phase pure HA. Poor adhesion is also a concern with thesefilms. Finally, control of electrochemical currents on porous implantswith irregular particles is challenging, making this process difficultto scale.

Biomimetic processes have also been developed. These processes employsolutions mimicking body fluid concentrations and are typicallyperformed near body temperature. These processes can yield bone-likeapatite but require days or weeks to produce films a few microns thick.Attempts to increase rates associated with such methods have led tocomplications in reproducibly controlling pH, deposition rate, andaccretion rate compared to crystalline growth on the surface of theimplant. Films formed at higher rates have been found to containamorphous material. Uncontrolled deposition rate also makes it difficultto achieve target coating weights or thicknesses.

As described above, hydroxyapatite coatings may be applied to orthopedicimplants to enhance osteoconductivity using methods that are eitherrapid but lead to coatings having certain undesirable or unpredictableproperties or lead to more desirable products but can take days to form.What is needed is a conformal calcium phosphate coating that can berapidly formed and has a microstructure that lends itself to uniformdegradation over a period of several weeks without generatingparticulates.

SUMMARY OF THE DISCLOSURE

Several embodiments of the invention are described by the followingenumerated clauses:

1. An orthopedic implant comprising a metal surface and a groupcalciumphosphate layer disposed on at least part of the metal surface, whereinthe calcium phosphate layer has an average crystallite size of less thanabout 100 nm in the [001] direction.

2. An orthopedic implant comprising a metal surface and a calciumphosphate layer disposed on at least part of the metal surface, wherein,the calcium phosphate layer, when subjected to XRD, produces a (002) XRDpeak and a (112) XRD peak, and the (002) XRD peak has an intensity 1.5to 10 times greater than the (112) XRD peak.

3. An orthopedic implant comprising a metal surface and a calciumphosphate layer disposed on at least part of the metal surface, whereinthe calcium phosphate layer dissolves continuously for more than 2 hoursin vitro.

4. An orthopedic implant comprising a metal surface and a calciumphosphate layer disposed on at least part of the metal surface, whereinthe calcium phosphate layer is substantially free of carbonate asmeasured by infrared spectroscopy.

5. The orthopedic implant of any one of the preceding clauses, whereinthe coating has an average crystallite size of about 10 to about 100 nmin the [001] direction.

6. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has an average crystallite size of about 15nm to about 70 nm in the [001] direction.

7. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has an average crystallite size of about 50nm to about 100 nm in the [001] direction.

8. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer, when subjected to XRD, produces a (002) XRDpeak and a (112) XRD peak, and the (002) XRD peak has an intensity 1.5to 10 times greater than the (112) XRD peak.

9. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer, when subjected to XRD, produces a (002) XRDpeak and a (112) XRD peak, and the (002) XRD peak has an intensity 2 to5 times greater than the (112) XRD peak.

10. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer dissolves for more than 2 hours in vitro.

11. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer dissolves for more than 5 hours in vitro.

12. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer dissolves for more than 24 hours in vitro.

13. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer is resorbed in vivo within 6 weeks.

14. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises about 0 wt % to about 5 wt %carbonate.

15. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer is substantially free of carbonate asmeasured by infrared spectroscopy.

16. The orthopedic implant of any one of the preceding clauses, whereinthe coating is in contact with the metal surface.

17. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface comprises a metal oxide.

18. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface comprises titanium.

19. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface comprises a cobalt chromium alloy.

20. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface comprises a titanium oxide.

21. The orthopedic implant any one of the preceding clauses, wherein themetal surface comprises a titanate.

22. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface comprises sodium titanate.

23. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface is a porous metal oxide surface.

24. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface is a titanium surface that has been treated withhydroxide.

25. The orthopedic implant of clause 24, wherein the hydroxide has aconcentration of 1M or greater.

26. The orthopedic implant of clause 24 or 25, wherein the hydroxide hasa concentration of 2M or greater.

27. The orthopedic implant of any one of clauses 24 to 26, wherein thehydroxide is sodium hydroxide.

28. The orthopedic implant of any one of clauses 24 to 27, wherein thehydroxide is potassium hydroxide.

29. The orthopedic implant of any one of clauses 24 to 28, wherein thetitanium surface is not heat treated after being treated with thehydroxide.

30. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface has a thickness greater than about 50 nm.

31. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface has a thickness between about 50 nm and about 1 μm.

32. The orthopedic implant of any one of the preceding clauses, whereinthe metal surface has a thickness between about 50 nm and about 100 nm.

33. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises hydroxyapatite, and thehydroxyapatite has a crystallinity of greater than about 90%.

34. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises hydroxyapatite, and thehydroxyapatite has a crystallinity of about 70 wt % to about 100 wt %.

35. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has a phase purity of crystallinehydroxyapatite of greater than 90%.

36. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has a shear strength of about 20 MPa toabout 80 MPa.

37. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has a tensile strength of about 50 MPa toabout 100 MPa as determined according to ASTM F1147.

38. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer, in the absence of colorants, is transparentor translucent.

39. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has a Ca/P ratio of 1 to 2.

40. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer has a surface area of about 15 m²/g to about200 m²/g.

41. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer does not release particulates underphysiological conditions.

42. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises an apatite.

43. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises a hydroxyapatite.

44. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises calcium-deficient hydroxyapatite.

42. A method of treating a patient comprising administering to thepatient the orthopedic implant of any one of the preceding clauses.

Additionally, several embodiments of the invention are described by thefollowing enumerated clauses:

1. An osteoconductive composition comprising calcium phosphate, whereinthe calcium phosphate has an average crystallite size of less than about100 nm in the [001] direction.

2. An osteoconductive composition comprising calcium phosphate, whereinthe calcium phosphate, when subjected to XRD, produces a (002) XRD peakand a (112) XRD peak, and the (002) XRD peak has an intensity 1.5 to 10times greater than the (112) XRD peak.

3. An osteoconductive composition comprising calcium phosphate, whereinthe calcium phosphate dissolves continuously for more than 2 hours invitro.

4. An osteoconductive composition comprising calcium phosphate, whereinthe calcium phosphate is substantially free of carbonate as measured byinfrared spectroscopy.

5. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has an average crystallite size of about10 to about 100 nm in the [001] direction.

6. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has an average crystallite size of about15 nm to about 70 nm in the [001] direction.

7. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has an average crystallite size of about50 nm to about 100 nm in the [001] direction.

8. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate, when subjected to XRD, produces a (002)XRD peak and a (112) XRD peak, and the (002) XRD peak has an intensity1.5 to 10 times greater than the (112) XRD peak.

9. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate, when subjected to XRD, produces a (002)XRD peak and a (112) XRD peak, and the (002) XRD peak has an intensity 2to 5 times greater than the (112) XRD peak.

10. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate dissolves for more than 2 hours in vitro.

11. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate dissolves for more than 5 hours in vitro.

12. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate dissolves for more than 24 hours in vitro.

13. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate layer is resorbed in vivo within 6 weeks.

14. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate comprises about 0 wt % to about 5 wt %carbonate.

15. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate is substantially free of carbonate asmeasured by infrared spectroscopy.

16. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate is in contact with a metal surface.

17. The osteoconductive composition of clause 16, wherein the metalsurface comprises a metal oxide.

18. The osteoconductive composition of clause 16 or 17, wherein themetal surface comprises titanium.

19. The osteoconductive composition of any one of clauses 16 to 18,wherein the metal surface comprises a cobalt chromium alloy.

20. The osteoconductive composition of any one of clauses 16 to 19,wherein the metal surface comprises a titanium oxide.

21. The osteoconductive composition of any one of clauses 16 to 20,wherein the metal surface comprises a titanate.

22. The osteoconductive composition of any one of clauses 16 to 21,wherein the metal surface comprises sodium titanate.

23. The osteoconductive composition of any one of clauses 16 to 22,wherein the metal surface is a porous metal oxide surface.

24. The osteoconductive composition of any one of clauses 16 to 23,wherein the metal surface is a titanium surface that has been treatedwith hydroxide.

25. The osteoconductive composition of clause 24, wherein the hydroxidehas a concentration of 1M or greater.

26. The osteoconductive composition of clause 24 or 25, wherein thehydroxide has a concentration of 2M or greater.

27. The osteoconductive composition of any one of clauses 24 to 26,wherein the hydroxide is sodium hydroxide.

28. The osteoconductive composition of any one of clauses 24 to 27,wherein the hydroxide is potassium hydroxide.

29. The osteoconductive composition of any one of clauses 24 to 28,wherein the titanium surface is not heat treated after being treatedwith the hydroxide.

30. The osteoconductive composition of any one of clauses 24 to 29,wherein the metal surface has a thickness greater than about 50 nm.

31. The osteoconductive composition of any one of clauses 24 to 30,wherein the metal surface has a thickness between about 50 nm and about1 μm.

32. The osteoconductive composition of any one of clauses 24 to 31,wherein the metal surface has a thickness between about 50 nm and about100 nm.

33. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate comprises hydroxyapatite, and thehydroxyapatite has a crystallinity of greater than about 90%.

34. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate comprises hydroxyapatite, and thehydroxyapatite has a crystallinity of about 70 wt % to about 100 wt %.

35. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has a phase purity of crystallinehydroxyapatite of greater than 90%.

36. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has a shear strength of about 20 MPa toabout 80 MPa as determined according to ASTM F1044.

37. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has a tensile strength of about 50 MPa toabout 100 MPa as determined according to ASTM F1147.

38. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate, in the absence of colorants, istransparent or translucent.

39. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has a Ca/P ratio of 1 to 2.

40. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate has a surface area of about 15 m²/g toabout 200 m²/g.

41. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate does not release particulates underphysiological conditions.

42. The orthopedic implant of any one of the preceding clauses, whereinthe calcium phosphate layer comprises an apatite.

43. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate comprises a hydroxyapatite.

44. The osteoconductive composition of any one of the preceding clauses,wherein the calcium phosphate comprises a calcium-deficienthydroxyapatite.

Additionally, several embodiments of the invention are described by thefollowing enumerated clauses:

1. A method of forming a calcium phosphate coating, the methodcomprising contacting a metal surface with a supersaturated solutioncomprising calcium ions and phosphate ions and reducing the amount ofair in contact with the supersaturated solution during the coating step.

2. A method of forming a calcium phosphate coating, the methodcomprising contacting a metal surface with a supersaturated solutioncomprising calcium ions and phosphate ions wherein the pH of thesolution varies by less than 0.1 pH unit/hour during the contactingstep.

3. A method of forming a calcium phosphate coating, the methodcomprising contacting a metal surface with a supersaturated solutioncomprising calcium ions and phosphate ions wherein crystalline calciumphosphate forms on the metal surface at a rate of 0.1 μm/h to 3 μm/h.

4. The method of any one of the preceding clauses, wherein the metalsurface is a metal oxide surface.

5. The method of any one of the preceding clauses, wherein the calciumphosphate coating is formed on an orthopedic implant comprising themetal surface.

6. The method of any one of the preceding clauses, further comprisingreducing the amount of air in contact with the supersaturated solutionduring the coating step.

7. The method of any one of the preceding clauses, wherein the pH of thesupersaturated solution varies by less than 0.1 pH unit/hour during thecontacting step.

8. The method of any one of the preceding clauses, further comprisingallowing the pH to decrease during the contacting step by apredetermined value that is less than 0.15 pH units.

9. The method of any one of the preceding clauses, wherein crystallinecalcium phosphate forms on the metal surface at a rate of 0.1 μm/h to 2μm/h.

10. The method of any one of the preceding clauses, wherein the calciumphosphate is a calcium apatite.

11. The method of any one of the preceding clauses, wherein the calciumphosphate is a hydroxyapatite.

12. The method of any one of the preceding clauses, wherein the calciumphosphate is a calcium-deficient hydroxyapatite.

13. The method of any one of the preceding clauses, wherein the pH ofthe supersaturated solution is from about 7.5 to about 7.9.

14. The method of any one of the preceding clauses, wherein theconcentration of calcium in the supersaturated solution is from about1.4 mM to about 1.8 mM.

15. The method of any one of the preceding clauses, wherein theconcentration of phosphate in the supersaturated solution is from about2 mM to about 2.3 mM.

16. The method of any one of clauses 1 to 9, wherein the calciumphosphate is octacalcium phosphate.

17. The method of clause 16, wherein the pH of the supersaturatedsolution is about 6.9 to about 7.1.

18. The method of clause 16 or 17, wherein the concentration of calciumin the supersaturated solution is from about 0.5 mM to about 1.4 mM.

19. The method of any one of clauses 16 to 18, wherein the concentrationof phosphate in the supersaturated solution is from about 0.1 mM toabout 0.9 mM.

20. The method of any one of the preceding clauses, wherein the Gibbsfree energy change associated with the forming step is from about 8kJ/mol to about 8.4 kJ/mol when the forming step begins.

21. The method of any one of the preceding clauses, wherein the coatingforms at a rate per unit surface area from about 0.01 mg/hr·mm² to 0.03about mg/hr·mm².

22. The method of any one of the preceding clauses, further comprisingremoving the metal surface from the supersaturated solution after fromabout 0.5 hour to about 12 hours.

23. The method of clause 22, further comprising contacting the metalsurface, after the removing step, with an additional amount of thesupersaturated solution that has not contacted the metal surface.

24. The method of any one of the preceding clauses, wherein thetemperature of the supersaturated solution is from about 45° C. to about50° C.

25. The method of any one of the preceding clauses, wherein thetemperature of the supersaturated solution is from about 46.5° C. to47.5° C.

26. The method of any one of the preceding clauses, wherein thesupersaturated solution further comprises a salt and a buffer.

27. The method of clause 26, wherein the salt is sodium chloride and thebuffer is tris(hydroxymethyl)aminomethane.

28. The method of any one of the preceding clauses, further comprisingagitating the supersaturated solution during the contacting step.

29. The method of any one of the preceding clauses, whereinheterogeneous crystal growth occurs on the metal surface and homogeneouscrystal growth does not occur.

30. The method of any one of the preceding clauses, further comprisingforming a titanium layer on an implant body to form the metal surface.

31. The method of any one of the preceding clauses, further comprisingactivating the metal surface by contacting the metal surface with abase.

32. The method of clause 31, wherein the base is a hydroxide anion.

33. The method of any one of the preceding clauses, wherein the metalsurface is a titanium dioxide surface.

34. The method of any one of the preceding clauses, wherein the metalsurface is an activated metal surface.

35. The method of any one of the preceding clauses, wherein the metalsurface comprises a titanate.

36. The method any one of the preceding clauses, wherein the processoccurs under inert atmospheric conditions.

37. The method of any one of the preceding clauses, wherein the processoccurs under an argon atmosphere.

38. The method of any one of the preceding clauses, further comprisingadding a calcium solution to a phosphate solution to form thesupersatured solution, wherein the phosphate solution comprises sodiumchloride and a buffer.

39. The method of any one of the preceding clauses, wherein the calciumsolution and the phosphate solution are mixed at from about 15° C. toabout 35° C.

40. The method of any one of the preceding clauses, wherein the calciumphosphate coating is not further treated to increase crystallinity afterthe contacting step.

41. The method of any one of the preceding clauses, wherein the methodis validated for the amount of the calcium phosphate coating on themetal surface.

42. The method of any one of the preceding clauses, wherein the calciumphosphate coating is formed predominantly through heterogeneousnucleation such that the supersaturated solution remains visibly free ofturbidity during the contacting step.

43. The method of any one of the preceding clauses, wherein the calciumphosphate coating forms at a substantially continuous rate throughoutthe contacting step.

44. The method of any one of the preceding clauses, further comprisingdetermining the amount of the calcium phosphate coating based on theamounts of the calcium ions and the phosphate ions.

45. The method of any one of the preceding clauses, wherein at least twodeposition sequences are employed.

46. The method of any one of the preceding clauses, further comprisingdetermining the amount of the calcium phosphate coating based on the pHof the supersatured solution.

47. The method of any one of the preceding clauses, further comprisingdetermining the amount of the calcium phosphate coating based on theduration of the contacting step.

48. The method of any one of the preceding clauses, wherein the pH ofthe supersaturated solution varies by from about 0.01 to about 0.2 pHunit/hour during the contacting step.

49. The method of any one of the preceding clauses, wherein the coatingforms at a rate per unit surface area from about 0.01 mg/hr·mm² to 0.03about mg/hr·mm².

50. The method of any one of the preceding clauses, wherein the initialpH of the supersaturated solution is from about 7.5 to about 7.9, andthe temperature of the supersaturated solution is from about 38° C. toabout 60° C.

51. The method of any one of the preceding clauses, further comprisingheating the coating in a phosphate solution to mitigate surfacecracking.

52. The method of any one of the preceding clauses, further comprisingcontacting the coating with a supercritical fluid to mitigate surfacecracking.

53. An osteoconductive composition formed according to the method of anyone of the preceding clauses.

54. An orthopedic implant comprising an osteoconductive compositionformed according to the method of any one of the preceding clauses.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description and theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing the weights of hydroxyapatite coatings formedon crystalline and amorphous 50 nm- to 500 nm-thick titanium dioxide(TiO₂) coated substrates;

FIG. 2 is a scanning electron microscopy (SEM) image of a 200 nm-thickamorphous TiO₂ coating after treatment with hydroxide;

FIG. 3 is an SEM image of a 200 nm-thick crystalline TiO₂ coating thatwas not treated with hydroxide;

FIG. 4 is a grazing angle X-ray diffraction (XRD) spectrum overlay,showing spectra for 200 nm-thick amorphous TiO₂ coatings, with andwithout hydroxide treatment, and 500 nm-thick amorphous TiO₂ coatings,with and without hydroxide treatment;

FIG. 5 is a grazing angle XRD spectrum overlay, showing spectra for 200nm-thick crystalline TiO₂ coatings, with and without hydroxidetreatment, and 500 nm-thick crystalline TiO₂ coatings, with and withouthydroxide treatment;

FIG. 6 is an SEM image of a titanium layer that has beenelectrodeposited onto a CoCrMo core;

FIG. 7 is an image of a full scale coating vessel;

FIG. 8 is an SEM image of a SoDHA coating at 15000× magnification;

FIG. 9 is an SEM image of a SoDHA coating at 100× magnification;

FIG. 10 is an SEM image of a SoDHA coating at 400× magnification;

FIG. 11 is a chart showing a relationship between pH and the weight ofhydroxyapatite precipitate and octacalcium phosphate (OCP) precipitateover the course of their respective deposition processes;

FIG. 12 is a chart showing deposition rates at different surface areasfor a solution deposited hydroxyapatite (SoDHA) process;

FIG. 13 is a chart showing a relationship between coating rate and thechange in free energy associated with deposition for OCP films formed at47° C. and 48° C.;

FIG. 14 is a chart showing the Ca/P ratios of five samples createdaccording to the SoDHA process in the full scale deposition system shownin FIG. 7;

FIG. 15 is a chart showing the crystallinity of the hydroxyapatite inthe five samples described in FIG. 14;

FIG. 16 is a chart showing the percentage of crystalline hydroxyapatitein the materials formed by the SoDHA process in the five samplesdescribed in FIG. 14;

FIG. 17 is a chart showing the tensile strength of crystallinehydroxyapatite in the materials formed by the SoDHA process in the fivesamples described in FIG. 14;

FIG. 18 is a chart showing the shear strength of crystallinehydroxyapatite in the materials formed by the SoDHA process in the fivesamples described in FIG. 14;

FIG. 19 shows a hip stem coupon fixture used in the XRD characterizationstudy described herein;

FIG. 20A shows superimposed XRD scans for as coated SoDHA HA discs;

FIG. 20B shows 25° to 27° 20 of the superimposed XRD scans of FIG. 18A;

FIG. 21A shows multiple XRD scans of a scraped SoDHA HA powder mixedwith quartz powders;

FIG. 21B shows representative Rietveld refined XRD scans ofcrystallographic quantification carried out for SoDHA HA-quartz powdermixtures;

FIG. 22 shows an averaged representative XRD scan of SoDHA HA coateddiscs;

FIG. 23 shows multiple XRD scans of a scraped solution depositedoctacalcium phosphate (SoDOCP) OCP powder;

FIG. 24 shows a Fourier transform infrared spectroscopy (FTIR) spectrumof a scraped SoDHA HA powder;

FIG. 25 is a chart showing the dissolution rate of a SoDHA HA sample;

FIG. 26 is a chart showing the dissolution rate of a National Instituteof Standards and Technology (NIST) standard HA sample;

FIG. 27 shows DSC traces from scraped SoDHA powders showing nodiscernible exothermic peaks on heating;

FIG. 28 is an image of a canine proximal humeral having two implantstherein;

FIG. 29 is an image of a canine distal femur having an implant therein;

FIG. 30 is an image of a Gription™ Plasma Spray HA-coated implant in atest subject;

FIG. 31 is an image of a Gription™ SoDHA HA-coated implant in a testsubject;

FIG. 32 is chart showing residual coating area before and after 6 weeksof implantation in plasma spray HA-coated and SoDHA HA-coated implants;

FIG. 33A is an SEM image of an oven-dried SoDHA coating withoutpost-processing at 1000× magnification;

FIG. 33B is an SEM image of a hydrothermally treated SoDHA coating at1000× magnification;

FIG. 34 shows superimposed XRD scans of an oven-dried SoDHA coatingwithout post-processing and a hydrothermally treated SoDHA coating; and

FIGS. 35A and 35B show representative images illustrating a crackdensity quantification method.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit theinvention to the particular forms disclosed, but on the contrary, theintention is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theappended claims.

The present invention relates to calcium phosphate coated orthopedicimplants, such as hydroxyapatite (HA) and octacalcium phosphate (OCP)coated orthopedic implants, and methods of making the same. The calciumphosphate coatings described herein have a highly uniformmicrostructure. When the implants are used in a human or animal, thecalcium phosphate coating degrades uniformly over an extended period oftime without releasing particulates. In some embodiments, this is aperiod of 6 weeks or less. The coatings described herein also haveadvantageous adhesion and/or cohesion properties such as increasedtensile strength compared to prior coatings. Additionally, the calciumphosphate coatings described herein can be rapidly formed on a substrateby a controlled, but rapid, growth process that lends itself to processvalidation utilizing process diagnostics that allow determination oftotal coating weight on a batch of parts without having to measurecoating weights on parts.

Solution deposited ceramic coatings may be predisposed to crackingduring drying. As coating thickness is increased this effect may beexacerbated. In some instances, cracking may be observed for solutiondeposited hydroxyapatite (SoDHA) coatings as they are dried after beingformed. Two exemplary, independent methods to mitigate drying cracksthat are described herein include: (1) organic solvent exchange andsupercritical solvent extraction, and (2) re-precipitation crack healingvia hydrothermal treatment. It is to be understood that organic solventexchange and re-precipitation crack healing may be performed independentof each other or in combination.

The compositions and methods described herein may improve cementlessfixation of orthopedic implants for improved survivorship and expand useof cementless implants to procedures where cemented implants are thecurrent standard of care. One skilled in the art understands that thismay allow for reduced operating room time and decreased costs for healthcare.

Calcium Phosphate Coating

The calcium phosphate coatings may comprise HA or OCP. As used herein,HA includes but is not limited to calcium deficient hydroxyapatite(CDHA). In some embodiments, the HA described herein isnon-stoichiometric, such as CDHA. The HA may be of the formulaCa_(10-x)(PO₄)_(6-x)(HPO₄)_(x)(OH)_(2-x), wherein x is from about 0 toabout 2 or about 0.1 to about 2. It is to be understood that theformulas described herein describe stoichiometric equivalents. In someembodiments the HA is of the formula Ca₁₀(PO₄)₆(OH)₂. In someembodiments, the OCP is of the formula Ca₈H₂(PO₄)₆.5(H₂O). The HAcoatings have characteristic molar ratios of calcium to phosphate (Ca/Pratio). The Ca/P ratio may be from about 1 to about 2, about 1.2 toabout 2, about 1.3 to about 2, about 1.39 to about 2, about 1 to about1.8, about 1.2 to about 1.8, about 1.3 to about 1.8, about 1.39 to about1.8, about 1 to about 1.7, about 1.2 to about 1.7, about 1.3 to about1.7, about 1.39 to about 1.7, about 1 to about 1.649, about 1.2 to about1.649, about 1.3 to about 1.649, about 1.39 to about 1.649, or about 1.5to about 1.67. It is to be understood that coatings of OCP, CDHA, ormixtures thereof may be modified by adjusting calcium and phosphateconcentrations and pH in the solutions from which the HA coatings may beformed.

As further described below, the HA and OCP coatings are formable fromsupersaturated solutions that remain substantially free of turbidity,due to homogenous nucleation in solution, throughout the coatingprocess. In some embodiments, the HA and OCP coatings lack carbonate,which assists with pH control during coating formation. Withoutintending to be bound by theory, deposition from solutions substantiallyfree of turbidity due to homogenous nucleation is believed to play arole in HA coatings deposited with predictable coating rates and highcrystallinity, uniform microstructure, and enhanced biocompatibility. Insome embodiments, the wt. % carbonate in the coatings is about 0% toabout 25%, about 0% to about 20%, about 0% to about 15%, about 0% toabout 10%, about 0% to about 5%, about 0% to about 3%, about 0% to about2%, about 0% to about 1%, about 0% to about 0.1%, about 0.1% to about25%, about 0.1% to about 20%, about 0.1% to about 15%, about 0.1% toabout 10%, about 0.1% to about 5%, about 0.1% to about 3%, about 0.1% toabout 2%, about 0.1% to about 1%, about 1% to about 25%, about 1% toabout 20%, about 1% to about 15%, about 1% to about 10%, about 1% toabout 5%, about 1% to about 3%, about 1% to about 2%, about 2% to about25%, about 2% to about 20%, about 2% to about 15%, about 2% to about10%, about 2% to about 5%, or about 2% to about 3%. In some embodiments,the concentration of carbonate in the coatings is as measured byspectroscopic methods such as IR spectroscopy. The coatings may besubstantially carbonate-free. As used herein, “substantiallycarbonate-free” coatings refers to coatings that do not have adistinguishable carbonate peak between 1500 cm⁻¹ and 1300 cm⁻¹ whensubjected to IR spectroscopy.

The wt % of crystalline HA or OCP in the HA or OCP coatings describedherein is about 50% to about 100%, about 60% to about 100%, about 70% toabout 100%, about 80% to about 100%, about 90% to about 100%, about 50%to about 99%, about 60% to about 99%, about 70% to about 99%, about 80%to about 99%, about 90% to about 99%, about 50% to about 95%, about 60%to about 95%, about 70% to about 95%, about 80% to about 95%, or about90% to about 95%. Without intending to be bound by theory, it isbelieved that the coatings are formed by heterogeneous nucleation,resulting in coatings that primarily comprise crystalline HA or OCP.

The HA component of the HA coatings, or, alternatively, the OCPcomponent of the OCP coatings, has a high crystallinity as measured by,for example, differential scanning calorimetry (DSC). The crystallinityis greater than about 50%, greater than about 80%, greater than about90%, greater than about 95%, greater than about 96%, greater than about97%, about 80% to about 99.9%, about 90% to about 99.9%, about 95% toabout 99.9%, about 96% to about 99.9%, or about 97% to about 99.9%.

The HA component of the HA coatings or, alternatively, the OCP componentof the OCP coatings, has a high crystalline phase purity of itspredominant phase. The crystalline phase purity is greater than about80%, greater than about 90%, greater than about 95%, greater than about96%, greater than about 97%, about 80% to about 99.9%, about 90% toabout 99.9%, about 95% to about 99.9%, about 96% to about 99.9%, orabout 97% to about 99.9%. The high crystallinity and high crystallinephase purity of the HA component in the HA coatings enhancesbiocompatibility and homogenous degradation in vivo while avoidingparticulate release. In some embodiments, crystallinity is measured bydifferential scanning calorimetry (DSC).

The HA component of the HA coatings or, alternatively, the OCP componentof the OCP coatings, has low or no amorphous content. The amorphouscontent is less than about 20%, less than about 15%, less than about10%, less than about 5%, less than about 4%, less than about 3%, about0.1% to about 3%, about 0.1% to about 5%, about 0.1% to about 10%, orabout 0.1% to about 20%. The amorphous content may be too low to detect.In some embodiments, amorphous content is measured by differentialscanning calorimetry (DSC).

The crystal structure of the HA coatings can be characterized usingX-ray spectroscopy, such as X-ray powder diffraction spectroscopy. TheHA coatings exhibit several characteristic 20 diffraction angles whencharacterized by X-ray powder diffraction. The numbers shown inparenthesis are the Miller indices associated with each peak. The X-rayspectra of the HA coatings may exhibit 20 diffraction angles includingabout 26±2° (002), about 28±2° (102), about 32±2° (112), about 50±2°(213), and about 53±2° (004) or about 26±0.5° (002), about 28±0.5°(102), about 32±0.5° (112), about 50±0.5° (213), and about 53±0.5°(004). The X-ray spectra of the HA coatings may exhibit 20 diffractionangles including about 26±1° (002), about 28±1° (102), about 32±1°(112), about 50±1° (213), and about 53±1° (004). The X-ray spectra ofthe HA coatings may exhibit 20 diffraction angles including about25.58±0.1°, about 28.13±0.1°, about 31.75±0.1°, 32.17±0.1°, about49±0.1°, and about 53±0.1°. It is to be understood that the diffractionangles recited herein may be systematically shifted due to variations ininstrumentation.

The XRD spectra of the HA coatings have characteristic relativeintensities. As used herein, the relative intensity of a peak in an XRDspectrum refers to the intensity of a peak divided by the intensity ofthe most intense peak in the spectrum. The peaks associated with the(002), (211), (112), (202), (213), and (004) directions may haverelative intensities of 100%, 15.5-16.5%, 27-28%, 50.5-60.5%, 19-20%,16.5-17.5%, and 14-15%, respectively. Any one of the peaks associatedwith the (002), (211), (112), (202), (213), and (004) directions mayhave a relative intensity of 100%, 10-20%, 23-33%, 40-70%, 15-25%,12-22%, and 10-20%, respectively. In some embodiments, thehydroxyapatite layer has a ratio of XRD intensity ratio of the (002)peak: the (211) peak that is greater than about 1, greater than about1.25, greater than about 1.5, greater than about 1.75, greater thanabout 2.0, greater than about 2.5, greater than about 3.0, or greaterthan about 3.5.

The HA coatings can also be characterized using Fourier transforminfrared (FTIR) spectroscopy. The HA coatings exhibit FTIR bands atabout 1100 cm⁻¹, characteristic of PO₄ ³⁻. The HA coatings lack FTIRbands characteristic for carbonate between about 1400 to 1500 cm⁻¹.

HA coatings of the instant disclosure result in small crystallites sizesas determined by X-ray diffraction or scanning electron microscopy. Insome embodiments, the HA coatings are nanocrystalline. The averagecrystallite size in the [002] direction is from about 60 nm to about 80nm, about 65 nm to about 75 nm, about 66 nm to about 73 nm, or about 68nm to about 69 nm. The average crystallite size in the [200] directionis from about 10 nm to about 30 nm, about 15 nm to about 25 nm, about 16nm to about 23 nm, or about 18 nm to about 22 nm. The averagecrystallite size in the [210] direction is from about 40 nm to about 60nm, about 45 nm to about 55 nm, about 46 nm to about 53 nm, or about 48nm to about 52 nm. In some embodiments, the HA films have a crystallitesize in at least one direction that is less than the wavelength oflight, and the grains are bonded to one another without the presence ofa second amorphous or crystalline phase having a different refractiveindex. In such embodiments, the films are transparent or translucent.

HA coatings of the instant disclosure are highly porous and have highsurface areas. The surface area is about 5 m²/g to about 100 m²/g, about10 m²/g to about 75 m²/g, about 10 m²/g to about 50 m²/g, about 10 m²/gto about 200 m²/g, about 10 m²/g to about 150 m²/g, about 10 m²/g toabout 100 m²/g, about 50 m²/g to about 200 m²/g, about 50 m²/g to about150 m²/g, or about 50 m²/g to about 100 m²/g. The surface area may bedetermined using Brunauer-Emmett-Teller (BET) method. This surface areamay lead to significant improvements in adsorption of therapeutic agentsonto these coatings, as further discussed below. The increased loadingcapability may be utilized to tailor the dose and prolonged release ofthe therapeutic agents thereby increasing treatment efficacy.

The coatings described herein release calcium at a substantiallycontinuous rate or at a continuous rate over an extended period of timein vitro as measured by calcium electrodes as described in ASTM F1926.As used herein, a substantially continuous rate is a rate that changesby less than 20% each hour. As used herein, a continuous rate is a ratethat changes by less than 5% each hour. The coatings may release calciumat a substantially continuous rate for at least about 5 hours, at leastabout 10 hours, at least about 15 hours, at least about 20 hours, about5 hours to about 100 hours, about 5 hours to about 50 hours, about 5hours to about 30 hours, about 5 hours to about 25 hours, about 10 hoursto about 100 hours, about 10 hours to about 50 hours, about 10 hours toabout 30 hours, about 10 hours to about 25 hours, about 15 hours toabout 100 hours, about 15 hours to about 50 hours, about 15 hours toabout 30 hours, or about 15 hours to about 25 hours. The coatings mayrelease calcium at a continuous rate for at least about 5 hours, atleast about 10 hours, at least about 15 hours, at least about 20 hours,about 5 hours to about 100 hours, about 5 hours to about 50 hours, about5 hours to about 30 hours, about 5 hours to about 25 hours, about 10hours to about 100 hours, about 10 hours to about 50 hours, about 10hours to about 30 hours, about 10 hours to about 25 hours, about 15hours to about 100 hours, about 15 hours to about 50 hours, about 15hours to about 30 hours, or about 15 hours to about 25 hours.

The HA and OCP coatings described herein have high adhesion to asubstrate and have high cohesion compared to previously described HA andOCP coatings. Adhesion and cohesion can be quantified by measuringtensile and shear peak stress values. The coatings described hereinextend outward from a surface of an orthopedic implant. As used herein,shear stress is the stress component parallel to the bulk directionsurface, and tensile stress is the stress component away from the bulkdirection surface.

The shear peak stress of the HA or OCP coatings, as determined accordingto ASTM F1044, is about 10 MPa to about 150 MPa, about 10 MPa to about100 MPa, about 10 MPa to about 75 MPa, about 10 MPa to about 65 MPa, orabout 28.2 MPa to about 63.6 MPa. The tensile peak stress, as determinedaccording to ASTM F1147, is about 25 MPa to about 120 MPa, about 40 MPato about 120 MPa, about 50 MPa to about 120 MPa, about 60 MPa to about120 MPa, about 68 MPa to about 120 MPa, 25 MPa to about 100 MPa, about40 MPa to about 100 MPa, about 50 MPa to about 100 MPa, about 60 MPa toabout 100 MPa, about 68 MPa to about 100 MPa, 25 MPa to about 95 MPa,about 40 MPa to about 95 MPa, about 50 MPa to about 95 MPa, about 60 MPato about 95 MPa, about 68 MPa to about 95 MPa, 25 MPa to about 90 MPa,about 40 MPa to about 90 MPa, about 50 MPa to about 90 MPa, about 60 MPato about 90 MPa, or about 68 MPa to about 90 MPa.

The HA or OCP coatings may have an average thickness, as measured fromthe surface of the orthopedic implant to which it adheres, of about 1 μmto about 50 μm, about 1 μm to about 25 μm, about 1 μm to about 20 μm,about 1 μm to about 15 μm, about 1 μm to about 10 μm, about 1 μm toabout 8 μm, about 3 μm to about 50 μm, about 3 μm to about 25 μm, about3 μm to about 20 μm, about 3 μm to about 15 μm, about 3 μm to about 10μm, about 3 μm to about 8 μm, about 5 μm to about 50 μm, about 5 μm toabout 25 μm, about 5 μm to about 20 μm, about 5 μm to about 15 μm, about5 μm to about 10 μm, about 5 μm to about 8 μm, or about 7 μm.

When applied to porous ingrowth surfaces like porocoat or gription, theHA or OCP coatings may have a weight per unit surface area of about 1 toabout 100 mg/cm², about 1 to about 75 mg/cm², about 1 to about 50mg/cm², about 1 to about 25 mg/cm², about 1 to about 12 mg/cm², about 5to about 100 mg/cm², about 5 to about 75 mg/cm², about 5 to about 50mg/cm², about 5 to about 25 mg/cm², about 5 to about 12 mg/cm², about 7to about 15 mg/cm², about 7 to about 14 mg/cm², about 7 to about 12mg/cm², about 9 to about 15 mg/cm², about 9 to about 14 mg/cm², about 9to about 12 mg/cm², about 9 to about 11 mg/cm², about 9 to about 12mg/cm², or about 8 to about 12 mg/cm².

When an orthopedic implant coated with the HA or OCP coatings describedherein is used in a patient or animal (e.g. canine), the in vivoresorption rates are such that the HA or OCP coating is resorbed withinabout 3 to about 15 weeks, about 4 to about 15 weeks, about 5 to about15 weeks, about 6 to about 15 weeks, about 3 to about 14 weeks, about 4to about 14 weeks, about 5 to about 14 weeks, about 6 to about 14 weeks,about 3 to about 12 weeks, about 4 to about 12 weeks, about 5 to about12 weeks, about 6 to about 12 weeks, about 1 to about 6 weeks, or lessthan about 6 weeks.

In some embodiments, the HA or OCP coating further comprises one or moreadditional therapeutic agents. The coating may be doped with anadditional material for improved osteoconduction and/or delivery ofanti-infective materials.

The therapeutic agent may include proteins, lipids,(lipo)polysaccharides, growth factors, cytostatic agents, hormones,antibiotics, anti-infective agents, anti-allergenic agents,anti-inflammatory agents, progestational agents, humoral agents,antipyretic agents, and nutritional agents. The therapeutic agent may bean osteoinductive substance, osteoconductive substance, or a substancethat is both osteoinductive and osteoconductive.

Metal Surface

The calcium phosphate layers described herein are disposed about asurface of an orthopedic implant. The surface may be a metal surface,such as a titanium or CoCr alloy surface or a titanium dioxide (TiO₂)surface. In some embodiments, the outer surface of the metal layer isamorphous and the rest of the metal layer is crystalline. In otherembodiments, the entire metal layer is crystalline. For example, theinterface between the surface and the calcium phosphate coating maycomprise an activated layer from which the calcium phosphate coatingnucleates and grows outward. It is to be understood that the entiresurface may be coated with HA or the surface may be masked such that apredetermined part of the surface is coated with HA.

The surface may be an activated metal surface. For example, when themetal surface is a titanium surface, the surface may be activated toform a titanate outer surface, which facilitates nucleation andincreased adhesion between the titanium surface and the calciumphosphate coating. Activation of the titanium surface also facilitatescontrolled crystal growth of the calcium phosphate layer therefromwithout further heat treatment, as will be further described below. Insome embodiments, the native oxide or oxide produced by passivationprocesses, is converted to titanate by hydroxide treatment. In someembodiments, the titanate is sodium titanate. Alternatively, crystallineTiO₂ may be applied to the implant core. Such crystalline films induceHA or OCP nucleation without further treatment. In some embodiments, theimplant surface is comprised of something other than titanium alloys. Inthis case, activation may be accomplished by deposition of nm scalefilms of crystalline TiOx on the implant surface. Alternatively, thinamorphous TiOx layers may be deposited and converted to titanate byhydroxide treatment of the amorphous film. Additional means ofactivation include creating surfaces that contain COOH, NH₂, or othercharged moieties.

In some embodiments, the entire core of the implant is titanium. Inother embodiments, titanium is coated on at least part of an implantcore, which, in turn, is coated with a calcium phosphate coatingdescribed herein. The implant core may comprise a material such asCoCrMo or PEEK.

Alternatively, the implant may comprise any suitable material, such assilicon based materials, ceramic based materials, or polymer basedmaterials. Other contemplated materials include cobalt, chromium, iron,tantalum, niobium, zirconium, and alloys thereof (e.g., titanium alloysand tantalum alloys), as well as cobalt, cobalt-chromium alloys, andstainless steel. The implant may comprise biocompatible polymers,natural or synthetic polymers, such as polyethylene (e.g., ultrahighmolecular weight polyethylene or polyethylene oxide), polypropylene,polytetrafluoroethylene, polyglycolic acid, polylactic acid, otherpolysaccharides, and copolymers of any of the foregoing (e.g.,copolymers of polylactic acid and polyglycol acid), including tissueengineering scaffolds composed of synthetic polymers (e.g. poly HEMA)and biological macromolecules (e.g. collagen and chondroitin sulfate).

The metal or metal oxide layer may have a thickness of at least about 25nm, at least about 30 nm, at least about 35 nm, at least about 40 nm, atleast about 45 nm, at least about 50 nm, at least about 60 nm, at leastabout 70 nm, at least about 80 nm, at least about 90 nm, or at leastabout 100 nm. In some embodiments, the layer may have a thickness ofabout 25 nm to about 125 nm, about 30 nm to about 125 nm, about 35 nm toabout 125 nm, about 40 nm to about 125 nm, about 45 nm to about 125 nm,about 50 nm to about 125 nm, about 25 nm to about 100 nm, about 30 nm toabout 100 nm, about 35 nm to about 100 nm, about 40 nm to about 100 nm,about 45 nm to about 100 nm, or about 50 nm to about 100 nm. Films under100 nm may cease to display interference colors after hydroxideprocessing. The preferred thickness of the layer may be determined basedon the desired color profile of the orthopedic implant.

The crystal structure of the titanium surface can be characterized usingX-ray spectroscopy, such as X-ray powder diffraction. The titaniumsurfaces exhibit several characteristic 20 diffraction angles whencharacterized by X-ray powder diffraction. The X-ray spectra of titaniumfilms exhibit 20 diffraction angles at about 26°, about 28°, about 32°,about 49°, and about 53°.

The metal surface may be modified prior to being coated with the HAcoating. For example, the metal surface may be modified with respect tosurface roughness in order to facilitate the adherence of the apatitecoating to the biocompatible substrate. Possible methods of modifyingthe roughness of the metal surface include acid etching or gritblasting.

Titanium Oxide Formation and Activation

As discussed above, a titanium oxide layer may be formed on anorthopedic prosthetic surface. Preferable processes for TiO₂ layerformation are conformal (non-line of sight) and produce films thatstrongly adhere to a core. Atomic layer deposition has been shown to becapable of producing both amorphous and crystalline films that are welladhered and of uniform thickness. Sol-gel processes andelectrodeposition of TiO₂ films also may be utilized.

After the surface is formed or otherwise available, surface activationmay be performed to encourage nucleation and growth of calciumphosphate. Basic conditions may be applied to the titanium oxide surfaceto activate it. In some embodiments, the titanium surface is treatedwith a hydroxide source, such as sodium hydroxide. Hydroxide treatmentproduces a porous titanate surface on the metal that facilitatesnucleation and growth of calcium phosphate.

Solution Deposited Hydroxyapatite (SoDHA) Process

The calcium phosphate coatings described herein are formed on theactivated surfaces by deposition from supersaturated solutions. Atsufficiently optimized supersaturation values, stable nuclei form andgrow from active surfaces, resulting in the calcium phosphate coatingsdescribed herein. Without intending to be bound by theory, it isbelieved that the growth predominantly occurs by a heterogeneousnucleation mechanism rather than a homogeneous mechanism under theconditions further described below. The process results in a crystallinecalcium phosphate product, such as the coatings described above.

Calcium and phosphate solutions are prepared and adjusted to desiredconcentrations by dilution. The calcium and phosphate solutions aremixed together, resulting in a solution that is supersaturated withrespect to the desired calcium phosphate product. Orthopedic implantprecursors, which have activated surfaces, are contacted with thesupersaturated solution, resulting in calcium phosphate coatingformation at a reproducible rate, under solution conditions that do notresult in turbidity. In some embodiments, the substrate has acrystalline TiO₂ film surface, which is not necessarily activated. Insome embodiments, the substrate has an amorphous film surface that hasbeen treated with a base such as hydroxide. It is contemplated thatimplants may be masked to allow deposition only on selected portions ofthe implants.

Solution turbidity may be determined with the aid of optical sensorsthat evaluate the UV range. An Optek AS16F probe sensor operating at 430nm was utilized to detect turbidity due to homogenous nucleation insolution. Without intending to be bound by theory, coating at controlledrates is believed to have occurred primarily by heterogenous nucleation.

The degree of supersaturation in the coating solution depends on theactivities of Calcium, and Phosphate ions in solution, and solution pH.Activities depend in turn on solution concentration, speciation, andionic strength. The calcium and phosphate stock solutions are mixedtogether, resulting in a solution that is supersaturated with respect tothe desired calcium phosphate product. Orthopedic implants, which haveactivated surfaces, are contacted with the supersaturated solution,resulting in calcium phosphate coating formation at a rapid,reproducible rate.

Implants are coated in a solution that is supersaturated with respect toHA and OCP phases. In some embodiments, the supersaturated solutioncomprises Ca(NO₃), K₂HPO₄, KH₂PO₄, NaCl, andtris(hydroxymethyl)aminomethane (TRIS) buffer. The ratio of HPO₄²⁻/⁻H₂PO₄ may be selected to achieve the target solution pH. Othercounter-ions besides NO₃ and K may be utilized as those skilled in theart will appreciate. Calcium and phosphate concentrates may be obtainedwith a certified concentration and then diluted to workingconcentrations prior to blending to create the final supersaturatedsolutions.

The solutions used in forming HA include calcium cations at aconcentration of about 0.5 to about 1.5 mM, about 0.6 to about 1.5 mM,about 0.7 to about 1.5 mM, about 0.5 to about 1.3 mM, about 0.6 to about1.3 mM, about 0.7 to about 1.3 mM, about 0.5 to about 1.1 mM, about 0.6to about 1.1 mM, about 0.7 to about 1.1 mM, about 0.5 to about 1.05 mM,about 0.6 to about 1.05 mM, about 0.7 to about 1.05 mM, or about 0.62 toabout 1.05 mM. In some embodiments the calcium ion is Ca²⁺.

The solutions used in forming HA include phosphate anions at aconcentration of about 0.75 mM to about 1.75 mM, about 1.0 mM to about1.75 mM, about 1.25 mM to about 1.75 mM, about 0.75 mM to about 1.5 mM,about 1.0 mM to about 1.5 mM, about 1.25 mM to about 1.5 mM, about 0.75mM to about 1.35 mM, about 1.0 mM to about 1.35 mM, about 1.25 mM toabout 1.35 mM, about 0.75 mM to about 1.3 mM, about 1.0 mM to about 1.3mM, or about 1.25 mM to about 1.3 mM. In some embodiments the phosphateions are PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, or a combination thereof.

The solutions used in forming HA have a pH of about 7.5 to about 8,about 7.55 to about 8, about 7.6 to about 8, about 7.65 to about 8,about 7.5 to about 7.9, about 7.55 to about 7.9, about 7.6 to about 7.9,about 7.65 to about 7.9, 7.5 to about 7.85, about 7.55 to about 7.85,about 7.6 to about 7.85, about 7.65 to about 7.85, 7.5 to about 7.8,about 7.55 to about 7.8, about 7.6 to about 7.8, about 7.65 to about7.8, 7.5 to about 7.75, about 7.55 to about 7.75, about 7.6 to about7.75, about 7.65 to about 7.75, 7.5 to about 7.7, about 7.55 to about7.7, about 7.6 to about 7.7, about 7.65 to about 7.7, or about 7.684.The pH may be the pH at the beginning of the coating process for a givencoating iteration. The pH may be the pH when the solution is at 25° C.

The solutions used in forming OCP include calcium cations at aconcentration of about 1.0 to about 2.0 mM, about 1.0 to about 1.9 mM,about 1.0 to about 1.8 mM, about 1.2 to about 2.0 mM, about 1.2 to about1.9 mM, about 1.2 to about 1.8 mM, about 1.3 to about 2.0 mM, about 1.3to about 1.9 mM, about 1.3 to about 1.8 mM, about 1.45 to about 2.0 mM,about 1.45 to about 1.9 mM, or about 1.45 to about 1.8 mM.

The solutions used in forming OCP include phosphate anions at aconcentration of about 1.5 mM to about 2.6 mM, about 1.5 mM to about 2.4mM, about 1.5 mM to about 2.25 mM, about 1.7 mM to about 2.6 mM, about1.7 mM to about 2.4 mM, about 1.7 mM to about 2.25 mM, about 2.0 mM toabout 2.6 mM, about 2.0 mM to about 2.4 mM, about 2.0 mM to about 2.25mM, about 2.2 mM to about 2.6 mM, about 2.2 mM to about 2.4 mM, or about2.2 mM to about 2.25 mM.

The solutions used in forming OCP have a pH of about 6.75 to about 7.25,about 6.75 to about 7.20, about 6.75 to about 7.15, about 6.75 to about7.1, about 6.75 to about 7.05, about 6.8 to about 7.25, about 6.8 toabout 7.20, about 6.8 to about 7.15, about 6.8 to about 7.1, about 6.8to about 7.05, about 6.85 to about 7.25, about 6.85 to about 7.20, about6.85 to about 7.15, about 6.85 to about 7.1, about 6.85 to about 7.05,about 6.9 to about 7.25, about 6.9 to about 7.20, about 6.9 to about7.15, about 6.9 to about 7.1, about 6.9 to about 7.05, about 6.95 toabout 7.25, about 6.95 to about 7.20, about 6.95 to about 7.15, about6.95 to about 7.1, or about 6.95 to about 7.05. The pH may be the pH atthe beginning of the coating process for a given coating iteration.

In some embodiments, a buffer is included in the supersatured solutionto stabilize pH. In some embodiments, the buffer istris(hydroxymethyl)aminomethane (tris) buffer. The concentration of trisis from about 1 mM to about 10 mM, about 2 mM to about 10 mM, about 3 mMto about 10 mM, 1 mM to about 8 mM, about 2 mM to about 8 mM, about 3 mMto about 8 mM, 1 mM to about 6 mM, about 2 mM to about 6 mM, about 3 mMto about 6 mM, or about 5 mM.

A salt may be included in the supersatured solution to increase ionicstrength. In some embodiments, the salt is sodium chloride. Theconcentration of salt is from about 100 mM to about 200 mM, about 100 mMto about 175 mM, about 100 mM to about 160 mM, 125 mM to about 200 mM,about 125 mM to about 175 mM, about 125 mM to about 160 mM, 140 mM toabout 200 mM, about 140 mM to about 175 mM, or about 140 mM to about 160mM.

The temperature of the solution during the coating process is from about40° C. to about 50° C., 42° C. to about 50° C., 44° C. to about 50° C.,46° C. to about 50° C., about 40° C. to about 48° C., 42° C. to about48° C., 44° C. to about 48° C., 46° C. to about 48° C., 46.5° C. toabout 47.5° C., or about 47° C. Implants may be maintained at a processtemperature within 0.5° C.

HA is a sparingly soluble salt with a K_(sp) on the order of 10⁻¹²⁰, andthus has a very narrow “meta-stable zone” from which controlledheterogeneous nucleation may occur. Surprisingly, a window was found toexist, allowing for relatively stable supersaturated solutions toprecipitate crystalline HA onto an activated surface of an orthopedicimplant in a controlled manner. In identifying this window, it wasobserved that low supersaturated concentrations led to slow nucleationrates, while high supersaturated concentrations led to uncontrolled,fast nucleation rates, accretion, and inconsistent growth on thesubstrate. Without intending to be bound by theory, coating underconditions of excessive supersaturation is believed to occur primarilyby homogenous nucleation and accretion.

Various conditions, may lead to increased solution stability. In someembodiments, solutions are mixed at room temperature rather than thetemperature at which the deposition process takes place. In someembodiments, calcium stock solutions are added to phosphate stocksolutions containing NaCl and tris. In some embodiments, the temperatureof stock solutions is not below room temperature. In some embodiments,the solution is housed in a vessel having smooth walls rather than roughwalls.

Surprisingly, it was possible to identify a window of supersaturatedsolution concentrations or, alternatively, a window of Gibbs freeenergy, that allowed for controlled HA crystal growth in a desirabletimeframe. The solutions used in the SoDHA process were configured suchthat dG for formation of HA was from about 7 kJ/mol to about 9 kJ/mol, 7kJ/mol to about 8.8 kJ/mol, 7 kJ/mol to about 8.6 kJ/mol, 7 kJ/mol toabout 9.4 kJ/mol, 7 kJ/mol to about 8.2 kJ/mol, 7.2 kJ/mol to about 9kJ/mol, 7.2 kJ/mol to about 8.8 kJ/mol, 7.2 kJ/mol to about 8.6 kJ/mol,7.2 kJ/mol to about 9.4 kJ/mol, 7.2 kJ/mol to about 8.2 kJ/mol, 7.4kJ/mol to about 9 kJ/mol, 7.4 kJ/mol to about 8.8 kJ/mol, 7.4 kJ/mol toabout 8.6 kJ/mol, 7.4 kJ/mol to about 9.4 kJ/mol, 7.4 kJ/mol to about8.2 kJ/mol, 7.6 kJ/mol to about 9 kJ/mol, 7.6 kJ/mol to about 8.8kJ/mol, 7.6 kJ/mol to about 8.6 kJ/mol, 7.6 kJ/mol to about 9.4 kJ/mol,7.6 kJ/mol to about 8.2 kJ/mol, 7.8 kJ/mol to about 9 kJ/mol, 7.8 kJ/molto about 8.8 kJ/mol, 7.8 kJ/mol to about 8.6 kJ/mol, 7.8 kJ/mol to about9.4 kJ/mol, 7.8 kJ/mol to about 8.2 kJ/mol, about 8.0 kJ/mol to about8.4 kJ/mol, about 8 kJ/mol, about 8.2 kJ/mol, or about 8.4 kJ/mol.

Surprisingly, it was also possible to identify a window ofsupersaturated solution concentrations or, alternatively, a window ofGibbs free energy, that allowed for controlled OCP crystal growth in adesirable timeframe. The solutions used in the OCP process wereconfigured such that dG for formation of OCP was from about 2.5 kJ/molto about 4 kJ/mol, about 2.5 kJ/mol to about 3.7 kJ/mol, about 2.5kJ/mol to about 3.6 kJ/mol, about 2.5 kJ/mol to about 3.5 kJ/mol, about2.5 kJ/mol to about 3.45 kJ/mol, about 2.7 kJ/mol to about 4 kJ/mol,about 2.7 kJ/mol to about 3.7 kJ/mol, about 2.7 kJ/mol to about 3.6kJ/mol, about 2.7 kJ/mol to about 3.5 kJ/mol, about 2.7 kJ/mol to about3.45 kJ/mol, about 2.9 kJ/mol to about 4 kJ/mol, about 2.9 kJ/mol toabout 3.7 kJ/mol, about 2.9 kJ/mol to about 3.6 kJ/mol, about 2.9 kJ/molto about 3.5 kJ/mol, about 2.9 kJ/mol to about 3.45 kJ/mol, about 3kJ/mol to about 4 kJ/mol, about 3 kJ/mol to about 3.7 kJ/mol, about 3kJ/mol to about 3.6 kJ/mol, about 3 kJ/mol to about 3.5 kJ/mol, about 3kJ/mol to about 3.45 kJ/mol, about 3.1 kJ/mol to about 4 kJ/mol, about3.1 kJ/mol to about 3.7 kJ/mol, about 3.1 kJ/mol to about 3.6 kJ/mol,about 3.1 kJ/mol to about 3.5 kJ/mol, about 3.1 kJ/mol to about 3.45kJ/mol, about 3.2 kJ/mol to about 4 kJ/mol, about 3.2 kJ/mol to about3.7 kJ/mol, about 3.2 kJ/mol to about 3.6 kJ/mol, about 3.2 kJ/mol toabout 3.5 kJ/mol, about 3.2 kJ/mol to about 3.45 kJ/mol, or about 3.2kJ/mol to about 3.45 kJ/mol.

The dG for formation of OCP and HA and the relative supersaturations ofthe solutions with respect to both HA and OCP for some embodiments ofthe SoDHA HA process are listed Table 1. These representative values arenot limiting as to the possible values associated with the methodsdisclosed herein.

TABLE 1 Changes in Energy and Supersaturation Values for SoDHA HAProcess dG HA dG OCP SS OCP SSHA −8.06451 −3.11966 3.230353 20.72261−8.11148 −3.14875 3.265878 21.09168 −8.14687 −3.16101 3.280953 21.37415−8.16934 −3.18283 3.307977 21.55537 −8.24149 −3.25443 3.398208 22.14794−8.27348 −3.25519 3.399187 22.41587 −8.34018 −3.32947 3.495425 22.985−8.34495 −3.33445 3.501971 23.0262 −8.34869 −3.33828 3.507014 23.05862−8.3538 −3.34325 3.513581 23.10291

As further described below, the HA and OCP coatings are formable fromsupersaturated solutions that remain substantially free of turbidity dueto homogenous nucleation in solution throughout the coating process.Without intending to be bound by theory, deposition from solutionssubstantially free of turbidity due to homogenous nucleation is believedto play a role in HA or OCP coatings deposited with predictable coatingrates and having high crystallinity, uniform microstructure, andenhanced biocompatibility.

HA and OCP are very sparingly soluble salts with K_(sp's) on the orderof 10⁻¹²⁰ and 10⁻⁹¹ respectively. As such, HA and OCP have very narrow“metastable zones” from which controlled heterogeneous nucleation andgrowth can occur. Surprisingly, it was possible to identify windows ofsupersaturation levels and temperatures that allowed for controlled HAor OCP crystal heterogeneous nucleation and growth in a desirabletimeframe. At these supersaturation values, stable nuclei form and growfrom active surfaces, resulting in the calcium phosphate coatingsdescribed herein.

The SoDHA process additionally comprises agitating the solution when itis in contact with the substrate. Too little agitation during blendingof stock solutions may destabilize the solution. High shear agitationduring blending of stock solutions may destabilize the solution.Agitation may occur by stirring.

The process may include reducing the amount of air in contact with thesupersaturated solution. In some embodiments, the process may beperformed under inert atmospheric conditions, such as under an argon ornitrogen atmosphere. The inert atmosphere limits the dissolution ofcarbon dioxide into the supersaturated solution, which can change the pHwithout CaP precipitation, interfering with the use of pH as an internalprocess monitor. Under such conditions, the resulting hydroxyapatitecoatings are substantially free of carbonate.

The process occurs at a controlled, but relatively rapid coating rate.Coating rate can be described in terms of coating mass or coatingthickness. For a fixed number of implants in the coating solution,higher coating weights are obtained on implants with high specificsurface area like those coated with porous metal in-growth structures.Coating thickness however, is approximately independent of the specificsurface area of the implant. Finally, both mass and thickness basedcoating rates are a function of total surface area/coating solutionvolume as seen in FIG. 12.

The process deposits HA such that thickness increases at a rate of abouta rate of about 0.01 μm/h to about 10 μm/h, about 0.01 μm/h to about 5μm/h, about 0.01 inn/h to about 4 μm/h, about 0.01 μm/h to about 3 μm/h,about 0.01 μm/h to about 2 μm/h, about 0.01 μm/h to about 1 μm/h, a rateof about 0.1 μm/h to about 10 μm/h, about 0.1 μm/h to about 5 μm/h,about 0.1 μm/h to about 4 μm/h, about 0.1 μm/h to about 3 μm/h, about0.1 μm/h to about 2 μm/h, about 0.1 μm/h to about 1 μm/h, a rate ofabout 0.5 μm/h to about 10 μm/h, about 0.5 μm/h to about 5 μm/h, about0.5 μm/h to about 4 μm/h, about 0.5 μm/h to about 3 μm/h, about 0.5 μm/hto about 2 μm/h, or about 0.5 μm/h to about 1 μm/h.

The process deposits HA on Gription at a rate of about 0.005 mg/hr·mm²to about 0.09 mg/hr·mm², about 0.005 mg/hr·mm² to about 0.025 mg/hr·mm²,0.005 mg/hr·mm² to about 0.0225 mg/hr·mm², 0.005 mg/hr·mm² to about 0.02mg/hr·mm², 0.005 mg/hr·mm² to about 0.0175 mg/hr·mm², about 0.005mg/hr·mm² to about 0.015 mg/hr·mm², about 0.0075 mg/hr·mm² to about 0.09mg/hr·mm², about 0.0075 mg/hr·mm² to about 0.025 mg/hr·mm², 0.0075mg/hr·mm² to about 0.0225 mg/hr·mm², 0.0075 mg/hr·mm² to about 0.02mg/hr·mm², 0.0075 mg/hr·mm² to about 0.0175 mg/hr·mm², about 0.0075mg/hr·mm² to about 0.015 mg/hr·mm², about 0.025 mg/hr·mm² to about 0.09mg/hr·mm², about 0.01 mg/hr·mm² to about 0.025 mg/hr·mm², 0.01 mg/hr·mm²to about 0.0225 mg/hr·mm², 0.01 mg/hr·mm² to about 0.02 mg/hr·mm², 0.01mg/hr·mm² to about 0.0175 mg/hr·mm², or about 0.01 mg/hr·mm² to about0.025 mg/hr·mm².

The coating process may be a “Constant Composition” or “VariableComposition” process.

In a constant composition process, reactants that are consumed bydeposition of CaP on implants are semi-continuously added back to thedeposition solution throughout the coating process. The addition ofreagents is performed based on the drop in pH that corresponds toprecipitation of CaP from solution. Thus, the amount of process reagentsthat are added back to the deposition solution become a surrogate forthe amount of HA deposited on the implants. Without intending to bebound by theory, the equations that calculate the composition of the“titrant” (the solutions that are added back to the deposition vessel inresponse to a change in pH induced by CDHA precipitation) may be:

TCaNO3=(Nb)(W_(CaNO3))+(10−x)Ceff

TP=(Nb)(W_(PO4))+6Ceff

TNaCl=(Nb)(W_(NaCl))−(20−2x)Ceff

TKOH=(Nb)(W_(KOH))+(14−2x)Ceff

where Ceff is equal to the moles of CaP precipitated per Liter of addedtitrant and x is the non-stoichiometric coefficient in CDHA, Nb=numberof burets adding titrants to solution, and W is the concentration ofreactants in the supersaturated solution.

In the variable composition process, chemical driving forces forprecipitation are allowed to fall from their initial conditions by anamount that maintains a high range of driving force rather than aconstant high driving force as is accomplished by the constantcomposition process. When the low limit of driving force is reached bydepletion of some fraction of coating reagents by precipitation of CaPfrom solution, the coating solution is discarded and a new coatingsolution is added to the deposition process vessel. One embodiment ofthe variable composition process utilizes the quantitative relationshipbetween change in solution pH and the amount and composition of CaP thatprecipitates from the coating solution. This relationship can be used todetermine when to discard coating solutions and replace them with freshsolution as well as to determine the predetermined process endpointwhere CaP coating weights have been met. The amount of buffer isselected to lessen the pH reduction that accompanies CaP precipitationwhile allowing pH to reduce enough to allow the use of pH change as aninternal process diagnostic. In some embodiments, the pH measurementsmay be made intermittently rather than continuously. Coating rates areincreased at lower deposition sequence times with greater numbers ofcoating sequences. In some embodiments, the HA and OCP coating solutionslack carbonate, which may assist with the use of pH as a process monitoror control during coating formation.

Without intending to be bound by theory, the reactions are believed toproceed by the stoichiometry indicated by Table 2.

TABLE 2 Stoichiometry for HA and OCP Processes HA OCP Ca₁₀ (PO₄)₆ (OH)₂Ca₈ (HPO₄)₂ (PO₄)₄ −6 H₂PO₄ −2 HPO₄ −4 H₂PO₄ +12 H +2 H +8 H +14 H₂PO₄−14HPO₄ −8 HPO₄ +8 H₂PO₄ Totals +8 H₂PO₄ −14 HPO₄ −10 HPO₄ +4 H₂PO₄

As shown in Table 2, precipitation of calcium phosphate is accompaniedby a drop in calcium and phosphate concentrations, and a decrease in pH.These changes in concentration and pH result in a reduction in degree ofsupersaturation as the reaction progresses, along with a decrease indeposition rate.

The relationship between pH and amount of precipitate is scalable todifferent solution volumes. This relationship between change in pH andamount of phase precipitated may be utilized as a process monitor toensure that a predictable amount of precipitate is formed. The pH of thesupersaturated solution may be monitored to determine the extent ofcoating that has taken place. In some embodiments, the substrate iscontacted by the solution until one or more of the calciumconcentration, phosphate concentration, and pH decrease to apredetermined level.

Although nucleation rates, growth rates, and relative driving forces forSoDOCP and SoDHA change as calcium phosphate precipitates, a process wasdeveloped to minimize changes in these values as precipitation proceeds.The process used for coating the implants was a variable compositionprocess. As used herein, a variable composition process refers to aprocess that allows for change in thermodynamic variables over thecourse of the process. In the variable composition process describedherein, implants may be coated by multiple batches of solution, allowingion concentrations and pH to fall only to a predetermined level duringeach of the iterations. To reduce the extent of concentration changes,multiple sequential depositions were used, with each deposition sequencecomprising contacting the orthopedic implant with fresh solution. The pHchange associated with deposition may be reduced by buffering thesolution with a buffer, such as TRIS buffer.

In some embodiments, three sequential depositions were performed. For athree sequential deposition process, concentration changes during eachdeposition sequence are reduced by two thirds compared to one depositionsequence. In some embodiments, only one deposition sequence isperformed. In some embodiments, 2 or 3 deposition sequences areperformed. 1 to 10, 2 to 10, 3 to 10, 1 to 5, 2 to 5, or 3 to 5deposition sequences may be performed. In some embodiments, the numberof deposition sequences employed depends on the ratio of the surfacearea of the implant to the volume in the coating vessel. Larger implantsurface area/volume ratios may correspond with a larger number ofshorter coating sequences. Lower surface area/volume ratios maycorrespond with fewer sequences of longer duration per sequence. Thecombination of pH buffering and refreshing of solutions minimizes thechange in thermodynamic driving forces and may help to ensure that thesame calcium phosphate phase is produced throughout the depositionprocess.

The total contact time with the solution deposition composition inaccordance with the inventive method typically is about 30 minutes ormore. The total contact time preferably is about 8 hours or less. Morepreferably, the biocompatible substrate is subjected to multiplesequence contact times of about 1 minute to about 2 hours, about 1minute to about 1 hour, about 1 minute to about 30 minutes, about 5minutes to about 2 hours, about 5 minutes to about 1 hour, about 5minutes to about 30 minutes, about 2 hours or less, about 1 hour orless, or about 30 minutes or less. In general, longer total contacttimes and shorter coating sequences provide greater thicknesses of thebioactive hydroxyapatite coating. Additionally, the contact time isdependent on the number of bioactive substrates being coated at any onetime.

In some embodiments, the relationship between weight of precipitate andchange in pH is used to monitor the progression of the SoDHA process. Inadditional embodiments, the relationship between weight of precipitateand change in calcium and/or phosphate concentration may be used tomonitor the progression of the SoDHA process. In other embodiments, theprocess is performed for a predetermined amount of time and pH, calciumconcentration, and phosphate concentration are not monitored.

Similarly, in some embodiments, the relationship between weight ofprecipitate and change in pH is used to monitor the progression of theSoDOCP process. In additional embodiments, the relationship betweenweight of precipitate and change in calcium and/or phosphateconcentration may be used to monitor the progression of the SoOCPprocess. In other embodiments, the process is performed for apredetermined amount of time and pH, calcium concentration, andphosphate concentration are not monitored.

In some embodiments, a supercritical fluid may be employed to dry SoDHAcoatings. This process includes displacing water from a coating with anorganic solvent followed by supercritical fluid extraction. After SoDHAcoating formation, organic solvent exchange is performed by immersingcoated articles in the organic solvent for a predetermined period oftime. After displacement of the organic solvent in the coating, thecoated article is placed in a vessel where a supercritical fluid isintroduced. Next, the vessel is depressurized to atmosphere whilemaintaining the temperature above the critical temperature of thesupercritical fluid. In this way the supercritical fluid isdepressurized directly from a supercritical state to a gas, which avoidscreation of liquid capillary forces that may cause cracks.

In some embodiments, the organic solvent is an alcohol. For example, theorganic solvent may be methanol, ethanol, or isopropanol. In someembodiments, the supercritical fluid is supercritical CO₂ (scCO₂).

Additionally, in some embodiments, the SoDHA coatings may be exposed tohydrothermal re-precipitating conditions. After SoDHA coating formation,the coatings may be placed in a phosphate solution and heated. Thishydrothermal treatment may be performed at temperatures from about 50°C. to about 350° C., about 60° C. to about 350° C., about 70° C. toabout 350° C., about 80° C. to about 350° C., about 50° C. to about 150°C., about 60° C. to about 150° C., about 70° C. to about 150° C., about80° C. to about 150° C., about 50° C. to about 99° C., about 60° C. toabout 99° C., about 70° C. to about 99° C., about 80° C. to about 99°C., about 50° C. to about 95° C., about 60° C. to about 95° C., about70° C. to about 95° C., about 80° C. to about 95° C., about 50° C. toabout 90° C., about 60° C. to about 90° C., about 70° C. to about 90°C., about 80° C. to about 90° C., about 50° C. to about 85° C., about60° C. to about 85° C., about 70° C. to about 85° C., about 80° C. toabout 85° C., about 50° C. to about 80° C., about 60° C. to about 80°C., or about 70° C. to about 80° C. The coatings may be heated for timesfrom about 15 minutes to about 24 hours, about 15 minutes to about 4hours, about 15 minutes to about 3 hours, about 15 minutes to about 2hours, about 30 minutes to about 24 hours, about 30 minutes to about 4hours, about 30 minutes to about 3 hours, about 30 minutes to about 2hours, about 1 hour to about 24 hours, about 1 hour to about 4 hours,about 1 hour to about 3 hours, about 1 hour to about 2 hours, or about 2hours.

The methods described herein maximize the amount of material that growson the substrate, and minimize the amount that accretes onto the surfacefrom material homogeneously precipitated in suspension. Additionally,these methods provide for a controlled, predictable deposition rate,produce films with high adhesion and cohesion, and produce a uniformmicrostructure that degrades uniformly without release of particulates.Predictable deposition rates allow targeted film thicknesses to bereadily achieved. The methods also provide suitable coverage of porousstructures and are suitable for various implant geometries.

Definitions

As used herein, relative supersaturation of a product (S) is defined bythe following equation: S=[IAP/K_(sp)] ^(1/v), where IAP is the ionicactivity of the product, K_(sp) is the solubility constant of theproduct, and v is the number of ions in the unit formula of the product.

As used herein, Gibbs free energy change (dG) associated with a phasechange is defined by the following equation: dG=RT/v*ln[IAP/K_(sp)],where R is the universal gas constant, T is absolute temperature, IAP isthe ionic activity of the product, K_(sp) is the solubility constant ofthe product, and v is the number of ions in the unit formula of theproduct.

As used herein, relative supersaturation S, is equal to (IAP/Ksp)^(1/v).

As used herein, homogenous precipitation or homogenous nucleation refersto nucleation of a solid phase from a supersaturated solution that doesnot involve a foreign surface, resulting in a turbid supersaturatedcoating solution.

As used herein, heterogeneous precipitation or heterogeneous nucleationrefers to nucleation of a solid phase on an impurity phase from asupersaturated solution that is substantially free of turbidity duringthe deposition process.

As used herein, “octacalcium phosphate” or “OCP” refers to a calciumphosphate having the formula Ca₈(HPO₄)₂(PO₄)₄.

As used herein, supersaturated refers to a solution in which a solute isconcentrated beyond equilibrium. When concentration is above thesaturation point, the solution is said to be supersaturated.

As used herein, in vitro, in reference to dissolution studies, means ina tris buffered saline solution at pH 7.4, as described in ASTM F1926.

Example 1—Activation of CoCr by Atomic Layer Deposition of TiO₂ Films

TiO₂ films were prepared on CoCr grit blast surfaces by Beneq (Helsinki,Finland) by atomic layer deposition. The films were produced from TiCl₄and H₂O precursors. Amorphous films were produced at 90° C. andcrystalline (Anatase plus Rutile) films were produced at 200° C. Filmswere activated with hydroxide, according to the methods described inExample 3 (4 hrs, 5M NaOH, 60° C.). 500, 200, 100, and 50 nm amorphousfilms (500 A, 200 A, 100 A, and 50 A) and 500 and 200 nm crystallinefilms (500° C., 200° C.) were evaluated for their ability to formhydroxyapatite coatings according to the SoDHA method using nominalconcentrations, as further described in Examples 5 and 6.

HA coating weight for the samples ranged from about 6 mg to about 8 mg,as shown in FIG. 1. Both amorphous and crystalline films were able tonucleate HA after activation by strong base. Coating experiments showedthat deposition occurred for as deposited crystalline titanium oxide,but at lower rates than observed for NaOH etched amorphous orcrystalline titanium oxide.

A scanning electron microscopy (SEM) image of the 200 nm-thick,activated amorphous film, prior to HA coating is shown in FIG. 2. An SEMimage of the 200 nm-thick, activated crystalline film, prior to HAcoating is shown in FIG. 3. The characteristic titanate topography wasapparent on amorphous films. Films prepared over 100 nm thick showedinterference colors after hydroxide treatment.

Grazing angle X-ray diffraction (XRD) spectra were obtained foramorphous and crystalline titanium coatings at 200 nm-thick and 500nm-thick before and after activation with NaOH. The XRD spectra for theamorphous films are shown in FIG. 4. The XRD spectra for the crystallinefilms are shown in FIG. 5.

Example 2—Electrolytic Formation of TiO₂ Films on CoCr Alloy

An electrolyte solution of 0.05 M TiCl₄ and 0.25 M H₂O₂ in a mixedmethanol/water (3/1 vol %) solvent was prepared. The pH of the solutionwas fixed between 0.9 and 1.0. All chemicals were ACS grade. To preparethe electrolyte solution, TiCl₄ was slowly added to the solvent,followed by H₂O₂. During the addition of H₂O₂, an immediate color changefrom transparent to dark orange was observed, indicating the formationof a peroxo-complex. Electrolytes were stored at about 4° C. afterpreparation and pH measurement and, if necessary, pH adjustment.Electrodeposition was performed galvanostatically up to the desiredcharge density. The temperature was fixed by a cryostat to 0° C. Ahomemade Labview program (controlling a Xantrex XDC 300-20 power source)was built to control current charge density while recording voltage-timecurves. The applied charge density was fixed in the range form 2.5 C/cm²to 40 C C/cm². The current density was varied between −50 mA/cm² to −50mA/cm².

Good film uniformity was obtained in 0.05 M TiCl₄, 0.5 M H₂O₂ in a mixedmethanol/water (3:1 vol. %) solvent (pH=0.97). Good growth occurred at−1.1 V for 1 hour at 60° C. FIG. 6 is an SEM image showing a titaniumcoating electrodeposited under these conditions on a CoCrMo substrate.

Example 3: Titanium Surface Activation

1 inch diameter Ti6-4 disks coated with DePuy Gription porous metalcoating were cleaned and activated by the following steps. Disks wereset in a container with reverse osmosis (RO) water and alkalinedetergent for 15 min with a sonicator 2 times. Next, disks were set in acontainer with only RO water for 15 minutes with a sonicator 2 times. 4disks were placed in a 500 mL beaker and 200 mL of 5M NaOH was added.The disks were placed in secondary containment and a loose cap was setover the top of the beaker. The temperature of the beaker was set to 60°C. and held for 4 hrs. The desks were removed from the beaker and rinsedin RO water in a sonicator for 15 minutes 4 times. Disks were left in a60° C. oven overnight to dry. No effect of heat treatment of thisactivation layer on the tendency to promote nucleation and growth of CaPcoatings was found in the methods disclosed herein, and examplesreported below were performed without heat treatment of the activatedsurface. Coating experiments showed that deposition occurred forcrystalline titanium, but at lower rates than observed for NaOH etchedamorphous titanium.

Example 4: Stock Solution Preparation

Concentrate and stock solutions for HA coating of 1 inch diameter disksin a 1 L vessel were prepared by the following steps.

A 36 mM Ca solution was prepared. A clean 2-liter bottle was obtainedand a magnetic stir bar was placed in the bottle. 8.50194 g of Ca(NO₃)was weighed out and poured into the 2-liter bottle. The bottle waspurged with Argon for 3-5 minutes. 1000 mls of deionized (DI) water witha resistivity of 18 MΩ or higher was added to the bottle. The bottle wasplaced on stir plate and its contents were stirred until Ca(NO₃) wasfully dissolved. The solution was filtered using a 0.22 μm cell culturevacuum filter (Corning, Funnel Volume, 1000 mL; Receiver: 90 mm; PoreSize: 0.22 μm; PES, No.: 431098).

A 40 mM phosphate (PO) solution was prepared. A clean 2-liter bottle wasobtained and a magnetic stir bar was placed in the bottle. 5.444 g ofKH₂PO₄ was weighed out and poured into the 2-liter bottle. 19.0387 g ofTris and 273.675 g NaCl were weighed out and added to the bottle. Thebottle was purged with Argon for 3-5 minutes. 898.1 mL of 18 MΩ orhigher DI water was added. Using a manual pipette, 5.8 mL of 6N HCl wasadded to the bottle. The bottle was placed on a stir plate and stirreduntil the Tris, NaCl, and KH₂PO₄ were fully dissolved. The final volumeof the solution was 1 L and the pH of the solution was approximately8.23 at 25° C. If necessary, pH may be adjusted to this value using HClor NaOH. The solution was filtered using a 0.22 um cell culture vacuumfilter (Corning, Funnel Volume, 1000 mL; Receiver: 90 mm; Pore Size:0.22 um; PES, No.: 431098).

495.3 mls of a 2.0787 mM Ca stock solution was prepared. The previouslyprepared 36 mM calcium solution was placed on a stir plate and stirredfor five minutes. A clean 1-liter bottle was purged with Argon. 28.6 mLof 36 mM calcium solution was added using a pipette. 466.7 mL of 18 MΩor higher DI water was added.

500 mL of 2.5690 mM P_(i) stock solution was prepared. The previouslyprepared 40 mM phosphate solution was placed on stir plate for fiveminutes. A clean 1-liter bottle was purged with Argon. 32.112 mL of 40mM phosphate solution was added using a pipette. 467.888 mL of 18 MΩ orhigher DI water was added.

A 1.7792 mM Ca solution was prepared. The previously prepared 36 mMcalcium solution was placed on a stir plate and stirred for fiveminutes. A clean 1-liter bottle was purged with Argon. 36 mM calciumsolution and 18 MΩ DI water were mixed to achieve the desiredconcentration.

A 2.2262 mM 500 mL P_(i) solution was prepared. The previously prepared40 mM phosphate solution was placed on stir plate for five minutes. Aclean 1-liter bottle was purged with Argon. 40 mM phosphate solution and18 MΩ DI water were mixed to achieve the desired concentration.

Example 5: HA Coating by Solution Deposition in 1 L Vessel

1 inch diameter porous metal coated titanium coupons were coated. Acover for a 1 L jacketed vessel was provided to allow for an Ar covergas during process the deposition process. 500 mLs of 2.569 mM phosphatestock solution prepared according to Example 4 was added into the 1 Ljacketed vessel, and the vessel was placed on a stir bar plate. The stirbar was turned on at 200 rpm. Next, 495.3 mL of 2.0787 mM Ca stocksolution, prepared according to Example 4 was poured into the vessel.Total volume at 25° C. was 1 L due to volume expansion associated withNaCl dilution. pH of the solution was 7.68 and the calculated dG (OCP)was approximately 3.25 and dG (HA) was approximately 8.24. Relative SSfor OCP and HA were about 3.3 and 22.5 respectively at the initiation ofthe coating process. A heated water bath was circulated through thejacketed vessel, and the solution was allowed to reach 47° C. Thetemperature was controlled within 0.5° C. Temperature sensors werecalibrated to a NIST traceable RTD. The etched (activated) disks wereplaced in fixtures that allowed disks to be suspended in the 1 Ljacketed vessel. After coating, the disks were moved into a firstcontainer of DI water and allowed to soak for 1 minute. Next, the diskswere moved from the first container to a second container of DI waterand allowed to soak for 1 minute. Then, disks were moved from the secondcontainer to a third container of DI water and allowed to soak for 1minute. After soaking, the disks were moved to a 6-well tray and placedin a 60° C. oven to dry for 60 min.

Example 6: Full Scale Process Validation

The nominal process described in Example 5 was repeated using a “fullscale” system shown in FIG. 7. The full scale system is designed to coatup to 40 acetabular cups or 16 hip stems in a single coating run of oneor more coating sequences. A series of coating runs were made utilizingboth standard DePuy TriLock BPS hip stems or hip stems modified toaccept one-inch diameter coupons (shown in FIG. 19) were made at nominalas well as + and − process limits. Process limits were defined as + and−2% of Ca and Phosphate concentrations and +−0.06 pH units. Coatingswere characterized by various methods as described in the examples.

Example 7: OCP Coating by Solution Deposition

The 1 L process described in Example 5 was repeated, except for thefollowing modifications. A 1.7779 mM Ca solution was used instead of the1.0284 mM Ca solution, and a 2.2262 mM P_(i) solution was used insteadof the 1.2730 mM P_(i) solution. The pH of the P_(i) solution was suchthat after combining the Ca and P_(i) solutions, the resulting solutionhad a pH of 7.000. The coating process was repeated using differenttotal deposition times to generate the experimental coating weightsshown in FIG. 11. Samples were characterized by XRD as described inExample 11.

Example 8: Use of dpH as a Process Monitor

pH and precipitate mass were monitored for the SoDHA process describedin Example 5 at nominal values, the SoDHA process described in Example 5at nominal values without tris, the SoDHA process described in Example 5at nominal values with 5 mM, the OCP process described in Example 7, andthe OCP process described in Example 7 with 5 mM tris. The relationshipbetween pH and amount of precipitate is scalable to different solutionvolumes and buffer strengths using a solution thermodynamics softwaresuch as “Chemist” version 1.0.3 from Micromath Scientific Software, 9202Litzsinger Road Saint Louis, Mo. 63144. This relationship between changein pH and amount of phase precipitated may be utilized as a processmonitor to verify that a targeted amount of precipitate is formed. Aspreadsheet calculator was constructed based on the relationshipssummarized in Table 2 to calculate the concentrations and activities ofreactants as a function of amount of CaP phase precipitated. CaP phasesthat can be modeled by this calculator include stoichiometric HA,stoichiometric OCP, non-stoichiometric CDHA, and mixtures of HA or CDHAwith OCP. For each increment of CaP phase precipitated, the reducedreactant concentrations were input into Chemist, which calculates thesystem pH based on buffer type and levels being analyzed. FIG. 11 showspredicted vs experimental plots of pH as a function of total mgprecipitated of CaP comprised of:

1) CDHA of formul a Ca_(10-x)(PO₄)_(6-x)(HPO₄)_(x)(OH)_(2-x) with x=to1.0

a) without TRIS buffer

b) with 5 mM TRIS buffer

2) A mixture of 80% OCP and 20% CDHA with x=1.5 with 5 mM TRIS.

Experimental values in this plot are taken from samples preparedaccording to Examples 5 and 7.

Example 9: Characterization of HA Coating

FIG. 8 shows a scanning electron microscope (SEM) image of SoDHA HAcoated flat titanium disc at 15000× magnification. FIGS. 9 and 10 showscanning electron microscope (SEM) images of a SoDHA HA coated porousingrowth structure (Gription) at 100× and 400× magnification,respectively. It is seen the HA coating was continuous over the discsurface.

FIG. 12 shows the effect of substrates having various surface area (mm²)on deposition rate (mg/hr) at fixed dG, temperature, and degree ofagitation. Materials were coated with HA at nominal values in the fullscale deposition system, using nominal conditions as described inExample 5. It can be seen that coating rate decreased as surface areaincreased. This trend may be utilized to estimate coating time based onsurface area for a given substrate.

The density of bulk HA and OCP are similar at about 3.1 g/cm³. Depositsof HA prepared at nominal values according to Example 5 weighed 7 mgs onflat coupons, had a surface area of 5.07 cm², and had a thickness ofabout 7 microns, corresponding to an actual density of about 1.97 g/cm³and a porosity of about 36%.

FIG. 13 is a plot showing coating rate at various initial dG values forthe formation of OCP films according to Example 7. It can be seen that acorrelation between dG and coating rate was increased at 47° C. comparedto 48° C. Without intending to be bound by theory, this trend isbelieved to be a consequence of deposition rates declining at high dGvalues due to precipitation in solution rather than on the implant.

Example 10: Full Scale Process Characterization

The coating prepared according to the full scale system process ofExample 5 at nominal and process limit values met the followingspecifications:

Coating weight: 0.08 to 0.12 mg/mm² of projected surface area

% crystalline HA by Rietveld analysis: >70%

% of amorphous calcium phosphate: <detection limit by DSC, as describedin Example 14.

XRD crystallite size parameters:

1/β (200) 1.63+−0.13

1/β (002) 4.15+−0.10

1/β (210) 1.5+−0.10

Tensile adhesion as determined according to ASTM F1147 (measured on gritblasted flat): >68 MPa Ca/P ratio: 1.39 to 1.65

FIGS. 14-18 summarize data obtained from the full scale system evaluatedat nominal and process limit conditions. In all cases, the error barsare equal to 3 standard deviations of the data.

FIG. 14 shows the Ca/P ratio for HA coated materials prepared bydeposition in the full scale system according to Example 6 at nominaland process limits. Ca/P ratio was determined by wet chemical methods.“NIST” refers to National Institute of Standards and Technology standardhydroxyapatite.

FIG. 15 shows the crystallinity of the coatings as determined by XRD forHA coated materials prepared by deposition in the full scale systemaccording to Example 6 at nominal and process limits. Crystallinity wasdetermined based on areas under selected diffraction peaks on thecoating and compared to the same peak areas on the highly crystallineNIST standard. The balance of material not reported is not amorphous asfound in PSHA deposits. Crystallinity values less than 100% reflect thefine grain size of the films and the fact that grain boundaries aredisordered and do not contribute much to diffracted peak areas.Amorphous content is determined by DSC.

FIG. 16 shows the percentage of HA as crystalline material out of allcrystalline material in the HA coated substrates prepared by depositionin the full scale system according to Example 6. In other words, it is ameasure of the phase purity of the films.

FIG. 17 shows tensile adhesion as determined by ASTM F1147 of HA filmsprepared by deposition in the full scale system according to Example 6.

FIG. 18 shows shear adhesion as determined by ASTM F1044 of HA filmsprepared by deposition in the full scale system according to Example 6.

Example 11—XRD Characterization

In this example, SoDHA HA prepared by deposition in the full scalesystem according to Example 6 and SoDOCP coatings prepared according toExample 7, were characterized by XRD. The nominal conditions were usedto prepare both coatings.

Titanium discs (1″ diameter) were processed in the fixtures shown inFIG. 19. These fixtures were fabricated from Depuy Tri-Lock BPS size 7and 8 hip stem implants, and the discs are held into the recessed holeswith stainless steel set screws.

Discs (and fixtures) were activated according to Example 3, except using2.5N NaOH at 45° C. for 4 hours prior to coating in the full scaleprocess apparatus. A total of 16 flat discs were coated in 8 fixturesutilizing two, two hour coating sequences.

Four as coated discs were analyzed. Superimposed XRD plots, (FIGS. 20Aand 20B) show that the HA coating is phase pure HA (within the detectionlimits of the X-ray equipment) and the HA coating was highly textured inthe (002) crystal orientation. FIG. 20B shows the peak from 25 to 27°20. Superimposed XRD scans for the as coated SoDHA HA discs weremeasured with the background calculated and removed using PanalyticalX′Pert software. It is also noted that these observations are consistentwith discs activated under more aggressive NaOH exposure of 5N and 60°C.

Scraped SoDHA HA powders were analyzed by powder XRD using Rietveldanalysis, as shown in FIG. 21A. Care was taken to scrape the coated HAmaterial down to the Ti substrate without generating excessive Ticontamination in the powder. Due to the relatively low mass (6-8 mg) ofpowder on each of the coated flat substrates, it was desirable to scrape6 substrates to obtain approximately 15 mg of SoDHA powder. The mass ofSoDHA and quartz standard mixed as an internal standard are presented inTable 3. Compiled XRD scans (1 powder, 3 repeats) are shown for SoDHA HAin FIG. 21A.

TABLE 3 Calculated wt % quartz and SoDHA HA in prepared powder Massscraped Mass quartz SoDHA powder standard Wt % Wt % (mg) (mg) SoDHAquartz 22.6 5.5 80.43 19.57

Results presented in Table 4 show a measured crystalline HA content of80.28%. It is noted that the 100% intensity octacalcium phosphate (OCP)peak (010) that occurs at 4.72° 20 in a randomly oriented powder was notobserved in any of the SoDHA HA powder XRD traces. It is thereforeconcluded that there is little-to-no OCP in the scraped SoDHA HApowders, and any OCP calculated by the Rietveld model is likely anartifact of the XRD background curve at angles approaching 3° 20 (FIG.21B).

TABLE 4 Crystallographic composition from Rietveld analysis Compensatedfor Quartz content Crystallographically CrystallographicallyCrystallographically HA content disordered content XRD HA disorderedcomponent HA disordered component Ave Std Ave Std Run (wt %) (wt %) (wt%) (wt %) (wt %) Dev (wt %) Dev 1 62.6 16.9 77.96 21.05 80.28 2.19 19.221.75 2 64.7 15.3 80.57 19.05 3 66.1 14.1 82.32 17.56

Table 5 shows the measured 20° values, together with the relativeintensities of various peaks, as determined using XRD of the HA samples.Background was calculated and removed using Panalytical X′Pert software.The XRD peak indices for standard HA powder (PDF number 09-0432) areinserted for reference. The relative intensity of each the peak wascalculated as a percentage of the most intense peak in the scan. It isnoted that not all peaks published in the NIST SRM data were observed inthe as coated SoDHA HA coating due to preferred orientation in thecoating. It also is noted that the 100% intensity peak in a randomlyoriented powder is the (211) peak, occurring at 31.76° 20 (publishedNIST data SRM 2910a), whereas the 100% intensity peak observed for ascoated SoDHA HA discs is the (002) peak (and also the (004) peak at53.14° 20) occurring at 25.89° 20 (FIG. 22). The increased intensity ofthe (002) peak indicates highly oriented crystals orthogonal to the(002) plane.

TABLE 5 SoDHA XRD Peaks Relative intensity d 2θ (%) 002 25.89 ± 0.02 100102 28.13 ± 0.02 15.5-16.5 211 31.75 ± 0.02 27-28 112 32.17 ± 0.0250.5-60.5 202 34.05 ± 0.02 19-20 213 49.51 ± 0.02 16.5-17.5 004 53.29 ±0.02 14-15

The SoDHA samples were determined to have the average crystallite sizesshown in Table 6.

TABLE 6 SoDHA Crystallite Sizes Average crystallite size τ (nm) Sample τHA (200) τ HA (002) τ HA (210) Nominal 20.50 68.61 49.19

An XRD spectrum overlay of the OCP coatings is shown in FIG. 23. Table 7shows the measured 20° value, together with the relative intensity ofeach peak after the background was calculated and removed. The relativeintensity of each peak was calculated as a percentage of the mostintense peak in the scan.

TABLE 7 SoDOCP OCP XRD Peaks Relative intensity d-spacing 2θ (%) 0 1 0 4.67 ± 0.02 6-21 −1 0 −1 15.98 ± 0.02 4-11 0 0 2 26.01 ± 0.02 100 2 4 128.14 ± 0.02 5-11 0 −3 2 29.14 ± 0.02 6-12 2 6 0 31.57 ± 0.02 5-13

It is noted that the 100% intensity peak in a randomly oriented powderis the (010) peak, occurring at 4.72° 20 (published JCPDS 00-026-1056data), whereas the 100% intensity peak observed for as coated SoDHA OCPdiscs is the (002) peak occurring at 26.00° 20. The increased intensityof the (002) peak (and also the (004) peak at 53.5° 20) indicates highlyoriented crystals in the (002) plane.

Example 12—FTIR Characterization

An FTIR spectrum was obtained of the SoDHA HA prepared according toExample 5. The FTIR spectrum is shown in FIG. 24.

Example 13—Dissolution

Dissolution rates of the SoDHA coating and of a NIST hydroxyapatitereference material were determined by placing the samples in a trisbuffered saline solutions at pH 7.4 and measuring change in calciumconcentration. FIG. 25 shows the dissolution results for the SoDHA HAcoating, and FIG. 26 shows the dissolution results for the NISTstandard. While the NIST sample stopped releasing calcium after lessthan two hours, the SoDHA sample released calcium for more than 20 hourswith no clear dissolution plateau.

Example 14—Differential Scanning Calorimetry (DSC)

Differential Scanning calorimetry (DSC) has been previously investigatedto directly observe, and qualitatively measure, the thermalrecrystallization of amorphous calcium phosphate phases in plasmasprayed hydroxyapatite materials. It has been reported that amorphouscalcium phosphate recrystallizes by a series of exothermic reactionsthat occur at different temperatures (within the range of 500° C. and750° C.) and with different amplitudes dependent upon changes in theplasma spraying parameters (e.g. plasma power, feed rate, coatingthickness etc.). Reactions are seen by the exothermic peak atapproximately 500-550° C. (the crystallization of hydroxyl-richamorphous regions in the material), the exothermic peak at approximately600-650° C. (the diffusion of hydroxyl ions into hydroxyl-depletedregions), and the exothermic peak approximately 720-750° C.(crystallization of oxyapatite phase).

In this example, DSC was used to observe any phase transitions (e.g.recrystallization) that can occur in hydroxyapatite/calcium phosphatematerials as a consequence of impurities and/or amorphous phases onheating up to 725° C.

Solution deposited SoDHA HA powders prepared according to Example 5 werescraped from flat Ti64 witness coupons. Each powder material was testeda minimum of 3 times using the DSC. The Pyris DSC analysis software wasused to measure the peak areas and peak positions (between 550 and 710°C.) for all powder samples, and the resulting recrystallization energies(J/g) were calculated.

DSC analysis of SoDHA powders scraped from coated Ti witness coupons isshown in FIG. 27, which shows no discernible exothermic peaks onheating.

In the area of interest, i.e. 550° C. and 710° C., there were noexothermic peaks seen in the DSC heating curves generated for scrapedSoDHA powders, indicating very little, if any, glassy amorphous phases.Based on the DSC curves, there was less than 2 wt % glassy amorphousmaterial in the SoDHA powders tested. It was also observed that theSoDHA powders analyzed using DSC were a gray color coming out of thetest, indicating a small amount of titanium is removed from thesubstrates on scraping and subsequently oxidizes during DSC testing.

Example 15—Canine Study

The objective of the canine study was to assess the effect on implantfixation of calcium phosphate coatings when deposited on a commerciallyavailable titanium porous implant. The fixation performance was assessedby testing the push-out strength of the bone implant interface and byhistomorphometric analysis of bone ingrowth, bone apposition, and bonehealing of the gap region. In this study, the performance of the calciumphosphate coatings was compared to non-coated porous implants and thesame porous implant coated with a commercially available plasma sprayhydroxyapatite coating.

Implants were placed in cylindrical defects created in the cancellousbone of nine large, skeletally mature, mixed-breed hounds. A canine wasselected as a model for testing as the bone structure of canines closelyresembles human bone. The sites of implantation selected for this studyprovide a large volume of cancellous bone. A total of 9 dogs wereenrolled in this study. The dogs obtained from VBF (Madison, Ga.) werepurchased from Antech, Inc. The breed of dog was Mongrel. The nine dogswere between approximately 1 year and 3 years of age at the time ofenrollment, and weighed between 25 and 31 kg. All dogs enrolled in thestudy were intact males with the exception of one, which was female. Allnine dogs were deemed healthy upon arrival to VBF. Examination at SJTRIprior to surgery revealed no obvious abnormalities.

The effects of these coatings on implant fixation were assessed in both1 mm gap and line-to-line or exact fits, as they represent a range ofimplant to host bone fit scenarios that are encountered in total jointreplacement procedures in humans. Four defects per animal were createdin cancellous bone to create side-by-side regions with line-to-line and1 mm radial gap fits between the porous coated surface of 6 mm diameterimplants and the host bone. These defects were created bilaterally inthe proximal humerus and distal femur. Two additional defects per animalwere created in cancellous bone distal to the first defect in thehumerus, bilaterally, in order to place a single implant with a 1 mmradial gap fit. This was done due to the limitation on the number ofanatomical sites suitable for implantation of side by side implants inthis model.

The following test articles were used:

Gription™ with SoDHA HA coating (HA version of the SoDHA coating)—10 mmlength and 11 mm length, 6 mm diameter.

Gription™ with SoDHA OCP coating (octacalcium phosphate version of theSoDHA coating)—10 mm length and 11 mm length, 6 mm diameter

Gription™ without coating—10 mm length and 11 mm length, 6 mm diameter

Gription™ Plasma Spray HA (plasma spray HA coating)—10 mm length and 11mm length, 6 mm diameter

The animals in this study were handled and maintained in accordance withthe requirements of the Animal Welfare Act. Compliance was accomplishedby conforming to the standards in the Guide for the Care and the Use ofLaboratory Animals, ILAR, National Academy Press, revised 1996. Theanimals were evaluated daily for behavior, appearance, urination,defecation, respiration, eating, and mobility.

Dogs were housed according to AR020, Routine Care for Dogs. Cages incages with stainless steel runs, with approximately 24 square feet offloor space. Floors were elevated with vinyl coated expanded mesh floorsthat were removable for sanitation. Cages were hosed clean at least oncedaily or more frequently as needed to prevent accumulation of excreta.Animals may have remained in place during daily cleaning with measurestaken to assure that the animals remained dry. All cleaning ordisinfecting agents used in the vivarium were designated as USDA “FoodSafe” and approved for use by the Attending Veterinarian.

Sanitation of cages and holding rooms was performed using a pressurewasher or other approved agent every 2-6 weeks (frequency based onbiological monitoring). Animals were removed from the cage duringsanitation to prevent exposure to hot water or disinfectant solutions.All surfaces of the cage and the room were rinsed thoroughly whendisinfectant solutions were used.

Animals were acclimated as stated per AR045, Quarantine, Acclimation,Stabilization, and Enrollment. Section 6.1.4 of AR045 states “Dogs areobtained from USDA Class A dealers are held for acclimation forapproximately 3 days. Quarantine is not required.” As per AR045, dogswere obtained from a single vendor and were housed seperatelyoff-siteAnimals were held for at least 2 days for physiologicstabilization prior to the surgical implantation procedure.

As per AR020, Routine Care for Dogs, dogs were fed an amount appropriatefor their weight and activity according to USDA and National ResearchCouncil regulations. All feed was provided in stainless steel bowls. Allanimals not scheduled for a procedure were fed at least once daily.Animals scheduled for a procedure were fasted 12-24 hours before theprocedure. There were no known contaminants considered to interfere withthe validity of the study.

The animals on this study had free access to fresh clean water as perAR020, Routine Care for Dogs. There were no known contaminantsconsidered to interfere with the validity of the study.

All animals undergoing surgical procedures were given anesthesiamedications consistent with AR006, Use of Sedatives, Analgesics andAnesthetics. Animals received the following medications at implant aslisted in Tables 8a-8c.

TABLE 8a Pre-Operative Medications for all animals Medication DoseDuration Carprofen 100 mg IM At the time of sedation Atropine 1 mg IM Atthe time of sedation Hydromorphone 2.5 mg IM At the time of sedationPropofol 100-300 mg IV At the time of induction Dexmeditomidine 0.25-0.5mg IV As needed, at the time of sedation Atipamezole 2.5-5 mg IV or IMAs needed for reversal of dexmeditomidine

TABLE 8b Intra-Operative Medication Medication Dose Duration Isoflurane1.0-3.5% During implant procedure Cefazolin 1000 mg in 250 ml 0.9%During implant procedure Saline, CRI at 10 mg/kg/hr LRS and or 5ml/kg/hr IV During implant procedure NaCl Drip Cefazolin 500 mg IV AfterCRI, every 90 minutes during implant procedure Atropine 1-2 mg IV Asneeded, for bradycardia

TABLE 8c Post-Operative Medication Medication Dose DurationHydromorphone 2.5 mg IM Immediately post-operatively Buprenorphine0.3-0.45 mg IM Twice daily for first 24 hours Carprofen 50-75 mg IM orPO Twice daily for 4 days, then as needed for pain Cephalexin 1000 mg IMor PO Twice daily for 4 days

All dogs were monitored during the surgery for heart rate, respiration,pulse oximetry for oxygen saturation, expired carbon dioxide, bodytemperature and limb-lead electrocardiography.

The ipsilateral forelimb and pelvic limb were prepared and asepticallydraped for surgery. A 10 cm skin incision was made on the craniolateralaspect of the shoulder joint extending from the acromion to the proximalthird of the humerus. Hemorrhage was controlled with electrocautery.Superficial fascia was incised along the same plane. The acromial headof the deltoid muscle was undermined, mobilized, and retracted caudally.Just distal to the tuberosity from the teres minor on the craniolateralflat surface of the proximal humerus, a battery powered drill wasutilized to place a 2.4 mm guide pin oriented in a slightly proximaldirection from 90 degrees to the bone surface. The position of the pinwas evaluated fluoroscopically. Adjustments were made if necessary. Aguide pin drill guide was then utilized to place a second 2.4 mm guidepin parallel and 17 mm distal to the first pin. A counterboringcannulated drill bit was then utilized to overdrill the proximal 2.4 mmguide pins creating a stepped or counterbored 6/8 mm diameter,approximately 24 mm long cylindrical defect. An 8 mm cannulated drillbit was then utilized to overdrill the distal 2.4 mm guide pin to createa defect approximately 14 mm in depth. During slow drilling, salinelavage was used to mitigate thermal necrosis from drill bit friction.Each defect was gently lavaged to remove bone debris. The periosteumimmediately surrounding each defect was trimmed back 1-2 mm to preventit from being carried into the defect during test article placement.

The two defects of the humerus were implanted with a test/controlarticle such that the outer end of the implant was placed just below thecortical surface. First, a 6 mm diameter implant was placed into the 6mm diameter segment of the upper humerus defect to create a line-to-lineor exact fit between the implant and the cylindrical wall of the bonedefect. A second 6 mm diameter implant was then placed into the 8 mmdiameter segment of the upper humerus defect after first assembling 8 mmdiameter titanium spacers to the ends of the implant. A 6 mm diameterimplant with 8 mm diameter spacers was placed in the 8 mm diameter lowerdefect in the proximal humerus. When implanted, these spacers created acontinuous, 1 mm radial gap between the porous coated surface of theimplant and the bone defect. These spacers add 1 mm of length to eachend of the radial gap implant assembly. Thicker (2 and 3 mm) spacerswere also used for assembly to the lateral side of the radial gapimplant to ensure spacer contact with cortical bone for mechanicalsupport and to limit post-op bleeding when necessary. Test articles wereplaced in the proximal and distal defects and their positions recordedfluoroscopically.

The wound was then lavaged and closed in 3 layers, taking care toobliterate dead space as much as possible. The deep layer andsubcutaneous layers were closed with 3-0 Vicryl. 4-0 Vicryl was used ina subcuticular pattern to complete the closure.

Following aseptic hanging leg prep with Ioban barrier drape placement,an 8 cm skin incision was made on the lateral aspect of the stifle onthe same side, centered over the epicondyle. Hemorrhage was controlledwith electrocautery. The biceps fascia was incised and retracted alongthe same plane allowing incision into the joint capsule. An area on thedistolateral surface of the femur, just cranial and proximal to theorigin of the lateral collateral ligament was identified. A 2.4 mm guidepin was placed at a 90 degree angle to the long axis of the femur. Theposition of the guide pin was evaluated fluoroscopically and adjusted ifnecessary. A 6/8 mm counterboring, cannulated drill bit was thenutilized to create a lateral to medial cylindrical defect 24 mm indepth. Saline lavage was performed during and after drilling asdescribed previously. Periosteum immediately surrounding the cylindricaldefect was excised prior to test article placement. A 6 mm diameterimplant was placed into the 6 mm diameter segment of the defect,creating an exact fit between implant and the wall of the bone defect. Asecond 6 mm diameter implant was placed in the 8 mm diameter segment ofthe defect following assembly of 8 mm diameter spacers to each end ofthe implant creating a region with a 1 mm radial gap fit between theimplant and the wall of the defect. Following test article placement,the position of the implant was recorded with fluoroscopy. After woundlavage, the joint capsule was closed with 2-0 PDS, deep fascia wasclosed with 0-PDS in a simple interrupted pattern. Subcutaneous andsubcuticular layer closure was performed with 3-0 Vicryl.

There were two implant sites per side. At the proximal humerus, SoDHA HAand Gription were placed, as shown in FIG. 28. For the proximal humerus,upper (more proximal) and lower (more distal) were the relativepositions of two defects that were separated by 17 mm between theircenters. At the distal femur SoDHA HA and PS HA were placed, as shown inFIG. 29. All implants were successfully placed.

The dog was rotated to the other side and after aseptic prep and steriledraping. The identical procedures were repeated on the contralateralfore and hind limbs.

Animals were observed at least once daily and in a manner consistentwith ARO 11, Assessment and Documentation of Animal Health and Welfare.Specifically, dogs had general assessments of health consistent withcurrent standards of record-keeping in veterinary medicine format.

No evidence of infection was observed. Several animals had one or moreskin incisions dehisce, most likely secondary to licking. Bandages ande-collars were placed, but the animals removed them with ease. Someanimals had fluid build-up around one or more incisions postoperatively.Fluid analysis and bacterial culture of the fluid from these animalsrevealed nonsuppurative inflammation with primary differential diagnosisof a seroma. No evidence of infection was observed. CBC and serumchemistries revealed no significant abnormalities and no evidence of asystemic infectious process. No inflammation was grossly observed toextend beyond the dermal layer, and no bone reaction was observed radiographically or during gross necropsy. While endcaps detached from theimplants in two animals, the implants remained intact with no evidenceof loosening or migration which is suggestive of rigid fixation at theinitial implant site.

All animals were terminated after 6-weeks. Animals were euthanasizedusing 5-7 ml (1800 mg-2520 mg) of Euthasol which was in accordance withAR007, Euthanasia of Animals, and consistent with the Report of the AVMAGuidelines on Euthanasia, June 2007.

A gross necropsy of implant sites was performed by a veterinarypathologist. Implanted humeri and femurs were harvested, and dissectedfree of surrounding soft tissue. Samples were wrapped in saline-soakedgauze. Immediately following necropsy, ex vivo fluoroscopy images weretaken of each of the specimens in the anterior/posterior, longitudinaland transverse directions to visualize the implants within thecancellous bone. Implanted bones were excised at time of necropsy,placed in heat-sealed plastic bags, shipped on wet ice to Histion, Inc.(Everett, Wash.), and processed for either histological evaluation ormechanical testing as described in Examples 16-17. Specimens werewrapped in saline-soaked gauze and shipped to Histion, Inc. (Everett,Wash.) for histological analysis.

Example 16—Histology Results

The performance of the calcium phosphate coatings were compared to anon-coated porous implant and the same porous implant coated with acommercially available plasma spray hydroxyapatite coating. Fluoroscopicimaging revealed all implants were in place.

The results were consistent with successful implantation of coated anduncoated porous devices bilaterally in the proximal humerus and distalfemur with a follow-up period of 6 weeks. The postoperativecomplications observed in the study population have no effect on theintegrity of the study or its data. The study was successful in theutilization of this animal model to enable the comparison of porousimplants with and without various coatings designed to improve fixationin cancellous bone.

Remaining tissue was trimmed as necessary, fixed in 10% neutral bufferedformalin, and specimens containing the gap portions of each implant wereembedded in methyl methacrylate. Two ground transverse sections stainedwith Stevenel's Blue/van Gieson were produced from each specimen andevaluated quantitatively to determine percent bone within the porouscoating and percent bone within the gap area. Bone apposition to theouter perimeter (including inner surfaces contiguous with the outerperimeter) and total apposition (including perimeter apposition andapposition to surfaces within the interstices of the porous coating)measurements were taken from specimens placed in the upper proximalhumerus and distal femur only. Data from both sections were averaged.Averaged data were used to determine differences between groups by ANOVAand the Tukey multiple comparisons test. Implants placed in threedifferent locations were compared separately. In the upper proximalhumerus, Gription™ SoDHA HA and Gription™ SoDHA OCP implants werecompared to Gription™ Porous Coating implants. In the distal femur,Gription™ SoDHA HA implants were compared to Gription™ Plasma Spray HAimplants. Sections were also grouped according to location and evaluatedqualitatively to determine the cellular and tissue responses to eachimplant type.

Histomorphometric analysis was performed blind to treatment on eachslide. Low power digital images were captured of each section thatincluded the gap and an additional amount of tissue surrounding eachimplant. Static histomorphometric analysis was completed to determine %bone apposition to the implant surface, % bone within the porous coatingand % bone within the gap area. Ingrowth was measured as % total voids.Additional parameters evaluated include average coating thickness. Theresults, averaged over the various specimens are shown in Table 9 forSoDHA HA gap, SoDHA HA line-to-line, and Gription line-to-line implants.

TABLE 9 Histomorphometry Results % % Ingrowth Apposition Gap 21.485527216.19171 Line-to-Line 28.6462277 33.04744 Gription Line-to-Line34.1005268 26.80749

The histomorphometry results showed that bone ingrowth into the gap andthe porous coated surface at the upper proximal humerus implantationsite for the Gription™ SoDHA HA implant (about 14% ingrowth) was bettercompared to Gription™ SoDHA OCP and significantly better compared to theGription™ Porous Coating control group (about 8% ingrowth). Percent boneapposed to the outer perimeter and to the total implant perimeter wassignificantly better for the Gription™ SoDHA HA implant group (about17.5% apposition) compared to the Gription™ Porous Coating group (about4.5% apposition), with no significant difference between the Gription™SoDHA HA and Gription™ SoDHA OCP groups.

Additionally, bone ingrowth into the gap and the porous coated surfaceat the upper proximal humerus implantation site for the Gription™ SoDHAHA implant (about 14% ingrowth) was better compared to Gription™ PlasmaSpray HA (about 12% ingrowth). Images of the Gription™ Plasma Spray HAand Gription™ SoDHA HA implants are shown in FIGS. 30 and 31,respectively.

Additionally, residual coating area after 6 weeks of implantation wasmeasured based on quantitative image analysis of sectioned implants, asshown in FIG. 32. In contrast to the Gription™ Plasma Spray HA-coatedgap samples, the Gription™ SoDHA HA-coated samples had virtually noresidual coating area.

Qualitative analysis showed more bone apposition deep into the porouscoating with the Gription™ SoDHA HA group compared to the Gription™SoDHA OCP and Gription™ Porous Coating group, the latter of which showeda fair amount of fibrous tissue apposition to the metal substrate.Collectively, these data suggest that Gription™ SoDHA HA implantsperformed best at the upper proximal humerus site.

When comparing Gription™ SoDHA HA, and Gription™ Plasma Spray HAimplants placed in the distal femur, Gription™ SoDHA HA had the highestmean percent bone ingrowth into the gap and the porous coating of thegroups.

The qualitative results showed little or no evidence of residual HA onthe test implants by 6 weeks, and no evidence of particles, noinflammation, and no giant cells (GCs) surrounding any of the testimplants. In addition, radiographic results showed no evidence ofabnormal radiolucency surrounding any of the implants. Collectively,these data provide evidence that there is no safety issue associatedwith implantation of the test coatings through 6 weeks and suggest thatthe test HA coatings are largely absent by 6 weeks.

Gription™ SoDHA HA performed better than both Gription™ SoDHA OCP andGription™ Porous Coating (significantly better compared to this lattergroup for percent bone in the porous coating and the gap areas andpercent bone apposition to the porous outer and total perimeters) in theupper proximal humerus. Qualitative analysis showed little or noresidual test HA by 6 weeks. Based on a lack of inflammation, GCs,particles and radiolucency surrounding the implants, there was noadverse response to the implants or the test HA coatings detected at anyof the implant sites 6 weeks after implantation.

Example 17—Mechanical Tests

At total of 90 5 mm thick cancellous bone blocks were removed from theimplanted bones that were excised samples obtained in Example 15. Afterbeing radiographed to facilitate processing, specimens were trimmed toremove excess bone, including bone overgrowth at the insertion siteand/or around the spacer. Specimens were trimmed to leave not less than4 mm of bone surrounding the implant on all sides. Five millimeter-thickwafers were cut perpendicular to the long axis of each gap-fit implantand used for mechanical testing. Five millimeter-thick wafers were cutperpendicular to the long axis of each line-to-line fit implant formechanical testing. Once prepared, the mechanical test specimens werewrapped in saline soaked gauze, frozen at −70° C. and shipped togetheron dry ice to Histion (Everett, Wash.) for mechanical testing. Remainingportions of each trimmed specimen were fixed in NBF and used forhistology.

Specimens designated for histology were trimmed and then cutperpendicular to the long axis of the implant. Two (2) ground transversesections spaced approximately 200-400 μm from one another were producedfrom the region of interest (ROI) containing the gaps. Sections (n=108)were stained with Toluidine blue/Paragon stains or other appropriatestain(s) and evaluated histomorphometrically.

Static push-out testing was conducted on specimens at 1 mm/minute untila 75% drop in peak force. Tests were formed using a MTS Sintech 65/Gstatic test machine with a 2.5 kN load cell and 4.0 mm diameter pin.Each specimen consisted of a canine bone slice containing a formerlyimplanted peg that was cemented into a custom potting fixture. The MTSTestWorks (rev 4.08B) software was used to apply a compressive load at1.0 mm per minute until a 75% drop from peak load occurred.

Force and displacement were recorded peak stress and energy at peakforce was calculated for each specimen and sample. Table 10 serves as asummary of the canine push-out study, showing the average and standarddeviation stress for Gription, SoDHA HA, SoDHA OCP (alternatively SoDOCPOCP), and plasma spray (PS) HA and various implant locations. Both gapand line-to-line implants are illustrated.

TABLE 10 Push out Stress; Separated Left and Right Average Peak Stressand Standard Deviation (MPa) Gription SoDHA HA SoDHA OCP PS BA Fit SiteAVG SD AVG SD AVG SD AVG SD UNE L Humerus, Upper 3.73 1.26 2.83 0.213.60 0.40 R Humerus, Upper 4.34 0.11 4.36 1.92 3.77 2.13 L Humerus,Lower R Humerus, Lower L Femur 2.57 0.17 4.17 2.44 R Femur 4.06 1.783.98 1.37 GAP L Humerus, Upper 0.69 0.52 1.98 0.23 1.05 0.37 R Humerus,Upper 1.04 0.19 1.29 0.41 1.30 0.64 L Humerus, Lower 1.63 0.24 RHumerus, Lower L Femur 1.20 0.86 1.56 0.15 R Femur 2.28 0.16 2.49 1.08

Example 18—Organic Solvent Exchange and Supercritical CO₂ SolventExtraction

Coated Gription™ and grit blast-flat coupons are rinsed with DI waterafter forming the SoDHA coating as described in Example 6. Residualaqueous solvent is exchanged with ethanol 3 times within a soaking step.Soak periods studied are 1 and 20 hours. After organic solvent exchangein ethanol, coupons are the placed on a rack and inserted into a 100 mlstainless steel vessel. The coupons are covered with ethanol and the topvessel end-cap is closed. The CO₂ flow direction is from the top of thevessel and out the bottom. The vessel is pressurized to 100 bar withliquid CO₂ and the liquid ethanol is displaced with liquid CO₂ at roomtemperature at approximately 2 liters/minute of gaseous CO₂ flow. Thedisplacement time is approximately ½ hour. After all the ethanol isdisplaced, the vessel is heated to 38° C. and dried for 4 hours withsupercritical CO₂ at a flow rate of 5 liters/min gas. After the allotteddrying time of 4 hours, the vessel is depressurized to atmosphere whilemaintaining the temperature above the CO₂ critical temperature of 32° C.The depressurization is conducted at approximately 1 liter/minute gasflow rate and lasted approximately 1 hour.

Example 19—Re-Precipitation Via Hydrothermal Treatment of SoDHA

The SoDHA coated coupons prepared according to Example 6 were quicklytransferred from DI water to a glass bottle containing either 15 mL 40mM phosphate (Pi) syrup prepared according to Example 4 or 15 ml 2.2262mM mM Pi stock prepared according to Example 4. The glass bottle wasthen sealed with a cap. The hydrothermal treatment of SoDHA films wasperformed at 90° C. for 2 hours. After hydrothermal treatment, the SoDHAcoated coupons were rinsed with DI water excessively for one minute andplaced in a 60° C. oven to dry for 1 hour.

The surface morphologies of the SoDHA and hydrothermally treated SoDHA(SoDHA-HT) films were examined by a scanning electron microscope(FE-SEM, Quanta 600 F). Scanning electron microscopy images for SoDHAand SoDHA-HT are shown in FIGS. 33A and 33B, respectively. The phasecomposition of the SoDHA and SoDHA-HT films was identified by X-raydiffractometry (Philips Analytical), using Cu Kα radiation at 45 kV, 40mA. The XRD patterns of the SoDHA film and the SoDHA film(hydrothermally treated in Pi stock at 90° C. for 2 hr) were collectedbetween 4°-60° (20) at 0.02° step and 0.01°/s, as shown in FIG. 34. TheXRD results revealed that hydrothermal treatment does not introduce newphases.

Example 20—Crack Quantification

The crack improvement benefit of post treatment according to Examples 18and 19 was quantified using image analysis by measuring the number ofcrack intersections on a predetermined horizontal grid. Images weretaken at 1000× on the FEI Quanta 600 F SEM, and then imported into theAxio Vision software (AxioVision SE64 Release 4.9.1.0, from Carl ZeissMicroscopy GmbH) and 25 horizontal grid lines 193.5 μm in length andvertically 6 μm apart were placed over most of the image. The interceptsof the cracks in the image and grid lines were then manually marked. Theintercepts were chosen manually by the operator to eliminate softwaredriven errors. The number of intersections in this given area was usedas a quantitative measure of the extent of surface cracking of SoDHAcoatings. Representative images illustrating the method are shown inFIGS. 35A and 35B.

Nominal SoDHA with optimized hydrothermal treatment parameters exhibitedminimal cracking, with fewer than 50 intercepts. The number of crackintersections and intercept density for representative regularly driedand post-processed coatings are shown in Table 11.

TABLE 11 Average crack intercept counts and crack intercept densitycomparison with and without post-processing Average number of Averageintercept density Sample intercepts (intercepts/mm²) Gription Disk -Nominal SoDHA 137 3659 no post-processing step Gription Disk - NominalSoDHA - 50 1335 2 hour hydrothermal treatment, 90° C. in phosphate stocksolution

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only the illustrative embodiments have been shownand described and that all changes and modifications that come withinthe spirit of the invention are desired to be protected.

There is a plurality of advantages of the present invention arising fromthe various features of the HA and OCP coatings described herein. Itwill be noted that alternative embodiments of each of the coatings ofthe present invention may not include all of the features described yetbenefit from at least some of the advantages of such features. Those ofordinary skill in the art may readily devise their own implementationsof calcium phosphate coatings that incorporate one or more of thefeatures of the present invention and fall within the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. A method of forming a calcium phosphate coatingon a surface of an orthopedic implant, the method comprising: contactingthe surface of the orthopedic implant with a supersaturated solutioncomprising calcium ions and phosphate ions, wherein the calciumphosphate coating on the surface of the orthopedic implant has a surfacearea of about 15 m²/g to about 200 m²/g.
 2. The method of claim 1,wherein the calcium phosphate coating on the surface of the orthopedicimplant is formed predominantly through heterogeneous nucleation suchthat the supersaturated solution remains visibly free of turbidityduring the contacting step and crystalline calcium phosphate forms onthe surface at a rate of 0.1 μm/h to 3 μm/h.
 3. The method of claim 1,wherein the pH of the supersaturated solution varies by less than 0.1 pHunit/hour during the contacting step.
 4. The method of claim 3, furthercomprising determining the amount of the calcium phosphate coating onthe surface of the orthopedic implant based on the amounts of thecalcium ions and the phosphate ions.
 5. The method of claim 1, whereinthe Gibbs free energy change associated with the forming the calciumphosphate coating on the surface of the orthopedic implant decreasesduring the contacting step.
 6. The method of claim 1, wherein the stepof contacting comprises at least two deposition sequences.
 7. The methodof claim 6, wherein each of the at least two deposition sequence isperformed for up to about 35 minutes.
 8. The method of claim 1, whereinthe calcium phosphate coating on the surface of the orthopedic implant,when subjected to XRD, produces a (002) XRD peak and a (112) XRD peak,and the (002) XRD peak has an intensity 1.5 to 10 times greater than the(112) XRD peak.
 9. The method of claim 1, wherein the supersaturatedsolution further comprises a salt and a buffer.
 10. The method claim 9,wherein the salt is sodium chloride and the buffer istris(hydroxymethyl)aminomethane.
 11. A method of forming a calciumphosphate coating on a surface of an orthopedic implant, the methodcomprising: contacting the surface of the orthopedic implant with asupersaturated solution comprising calcium ions and phosphate ions,removing the surface of the orthopedic implant from the supersaturatedsolution, and contacting the surface of the orthopedic implant, afterthe removing step, with an additional amount of the supersaturatedsolution that has not contacted the surface of the orthopedic implant.12. The method of claim 11, wherein the calcium phosphate coating on thesurface of the orthopedic implant has a shear strength of about 20 MPato about 80 MPa.
 13. The method of claim 11, wherein the calciumphosphate coating on the surface of the orthopedic implant has a tensilestrength of about 50 MPa to about 100 MPa as determined according toASTM F1147.
 14. The method of claim 11, further comprising adding acalcium solution to a phosphate solution to form the supersaturatedsolution, wherein the phosphate solution comprises sodium chloride and abuffer.
 15. The method of claim 14, wherein the calcium solution and thephosphate solution are mixed at about 15° C. to about 35° C.
 16. Themethod claim 11, further comprising heating the calcium phosphatecoating on the surface of the orthopedic implant in a phosphate solutionto mitigate surface cracking.
 17. The method claim 11, furthercomprising contacting the calcium phosphate coating on the surface ofthe orthopedic implant with a supercritical fluid to mitigate surfacecracking.
 18. The method of claim 11, wherein the surface of theorthopedic implant comprises a material selected from the groupconsisting of a metal, a metal oxide, a polymer, and a ceramic.
 19. Amethod of forming a calcium phosphate coating on an implant body, themethod comprising: forming a titanium layer on the implant body to forma metal surface on the implant body, activating the metal surface on theimplant body by contacting the metal surface on the implant body with abase, contacting the metal surface on the implant body with asupersaturated solution comprising calcium ions and phosphate ions,wherein the concentration of calcium ions in the supersaturated solutionis from about 0.9 mM to about 1.4 mM.
 20. The method of claim 19,wherein the base is a hydroxide anion.